The string section is the most used groups in the orchestra. For one thing, they don’t need to rest an embouchure, and the expressive quality of the strings is versatile so they get a lot of play time. If the look of 20 staves on a page all at once feels daunting to you then starting with just the 5 staves of strings would be recommended. You could even start with a string quartet and then only be looking at 4 parts. For any instrument you want to get to know the reasonable range of comfortable playing and also the absolute range for pushing the limits if you are writing for a group or player you know can handle it. You will also need to read the clefs and deal with transpositions. The strings don’t have any tricky transposition, the double bass sounds an octave lower than written but that’s easy to sort out in your head. The viola commonly plays alto clef which is the only strange thing about reading the strings. It takes a little getting used to but nothing any different than learning any other clef. I remember I learned treble clef first as a kid, then I learned bass clef when my voice changed and it wasn’t a big deal so there’s no reason to make a fuss over learning yet another clef (For my own benefit I made some alto clef flashcards in the form of a You-Tube video, use it if you like).
No better way to get your feet wet than to just jump in at this point so for a quick walkthrough I’ll give you a segment from Elgar’s Enigma Variations Number 9 “Nimrod”.
The first 8 bars are all string. There are definitely more simple examples than this but this just happens to be one that I was recently looking at. Notice right away that second violin, viola, and cello all split within the section, so it’s a pretty thickly harmonized section. Looking close at the divisi sections you see the parts criss-cross too, based on stem direction. Half the section will play notes with stems up, and the other half with stems down. Elgar has the melody in the first violins but he also has some secondary melodic movement that he wants to come through in the lower parts, that is why the second viola part is sometimes higher than the first viola. This melodic movement will not translate to a keyboard reduction though but it’s worth it to play through the individual lines to get a feel for the intended up and down motion.
Another observation is that some of the notes are doubled between two sections. The second and third notes of the lower 2nd violin are the same notes as the upper notes of the viola. An interesting choice to have a section divisi to a note that another section is already playing. One reason you might do this is to get a more rich tone, the sound of a violin playing an A is similar but not exactly the same as a viola playing an A but both together could thicken the tone but I think it’s a subtle effect. This will not make the ensemble louder, by the way, but it will spread the harmony spatially. The violas are usually seated to the right and the violins on the left, if they share this note then it’s coming from both sides and also the orchestra gets to hear more of the harmony from their closer neighbors so it would change the listening experience for the players too. These are just guesses, I don’t know what Elgar’s thoughts were but I’m guessing that he started writing some harmony parts with the secondary melodic function I mentioned earlier and then realized that there were a few places where that led to a missing chord tone and decided to remedy it by div. and then he just ran with it filling the whole middle range with it. This section just happens to have a lot of divisi but it’s totally fine to not use it. It’s common to not split the parts further than the standard 5 sections, no shame in that but put it in your toolbox because when you want to thicken the harmony a well played divisi will do the trick.
On the low end you see the 2nd cello part tracks the bass closely (remember bass will sound an octave lower for a note on the same position of the staff). Cello is the bass instrument of a string quartet and in the orchestra is has a versatile role where it can support the bass, it can fill in middle harmony, or it can take melodic passages too so look for examples of all of those roles. The 1st cellos are doubling the viola almost note for note during measures 3-7, so half the section gets to do a more melodic type of harmony role while the other half is playing a bass role. The basses have a good thick low end but cello can give those notes some definition so you not only feel some rumble but you can more easily interpret pitches with some of the higher frequency overtones.
Doing a full blown harmonic analysis is always a fun activity if you’re in to that sort of thing, and I hope that any composer who is interested in orchestration is into it. I don’t want to tell you what to do but it’s really going to help if you can analyze it. I have reduced these 8 bars to a grand staff that can be played on keyboard and it’s perhaps easier to digest in this format but you’ll get to a point where you’ll want to read a score and understand it without going through this step so I’m not going to say you should do this for every score you study, but do it a few times at least so you’ll have that skill for whenever you need it later. Most scores will have combined parts that can not be played by one person at a keyboard, there are just too many notes, so a keyboard reduction will need to take some liberties. The sound of a passage played at a piano will have a very different effect too, this Elgar example illustrates that vividly. It has a very different feeling when I play it at the piano. The strings are able to put way more syrup on it.
There is a notable use of the lydian mode, which comes across as F major and D minor type chords because of the A natural. You can think of it as F major playing a V/V type role but there are a few complex moments in there, in particular beat 3 of measure 6 I think is the strangest moment. It’s hard to find one exactly right definition of what’s happening here, there are a few ways to define it and I’m sure there are some theory buffs who will argue that there is one proper analysis but to me it’s all about passing tones that pretty smoothly take you from a D minor to a second inversion F chord by the second beat of measure 7. Dissecting each point along the way is not as important to me as the motion that gets you to the destination. From there to the end you get what could be a classic tin pan alley turnaround as I’ve blocked it out below but with the string arrangement notice how it sounds much more tender and reflective than when you play this cadence on the piano.
This is a view of my process, and all along the way I will listen to the recording and reverse engineer how you might get to this result in practice from having that sound in your head. You really want to make a connection between the sound of it and the dots on the page. The more you read and listen the better that connection will be.