I'm just curious... I've never really had a go at learning a stringed instrument. How does it work?

Because I thought that you put your finger higher or lower down the string, and the closer to the pegs, the lower the note.

And that's how you get the different notes, just depending on how "short the strings are"

Then my friend let me have a go on her cello yesterday, and taught me how to play the bass part of Canon. It was all "Press down one finger on the A string", "Do open D", "Put four fingers on that string".

And it wasn't a specific place on the cello string, just a finger, or two, or four

Then I said about moving up and down, and she told me that was 1st position, 2nd, 3rd, 4th.

She said she hasn't learnt that part yet (she's grade 3 apparently...)

So... there are only 4 places on the string where you put your fingers, and it's all about pressure?

I'm confused

First position on the violin is like this:
link here
Fingers are labelled 1 to 4, the specific place on the string they should go is the position that is the right note but depends how large your fingers are.
To go from 1st to 2nd position you move each finger one up so 1 moves where 2 was and 2 moves where 3 was etc.
Hope that helps!

That's all completely true.

To get actual notes (as opposed to random pitches somewhere in between), you have to put your fingers in certain places and there are standard fingers you would use for each note and its position (I assume you use more than 1 finger at once for the cello primarily because the strings are stronger and need more effort to be kept held down.)
So, rather than thinking in terms of lengths of strings, it is much easier to think in terms of 1st finger, 2nd finger etc. It DOES matter where you put your 4 fingers: you put them where you need them to be for the string to be the right length.

To get high notes, you can't keep your hand in 'first position' (hand closest to the pegs), so have to move to a higher position in order to be able to reach far enough to get the string short enough.

Sorry, that wasn't particularly well explained, but I hope it helped a bit.

The fingering for cellos is different though, but the priciple is the same - i.e. the notes get higher on each string as you move away from the pegs.

You do need to put your fingers in specific places to get specific notes (otherwise everything will be out of tune), but the are a lot of notes which can be fingered on different strings and postions. For example, on a violin the fourth finger on the D string in 1st position is an A and this is the same note as the open A string. On a cello, the 1st finger in 4th position (or 2nd finger in 3rd position, or alternative) on the D string is an A and this is the same as the open A string.

bobziekins - it sounds like your friend is maybe playing without entirely understanding what she's doing. It might help if you can get someone else to show you.

i wonder if her friend was just trying to explain it in simple terms--i believe it's common to start with 'first finger', 'second finger', instead of E, F#, etc? still, it is a specific place on the string, otherwise as Flossie says, the intonation will be all wrong. (and, btw, one of the advantages of a fretless string instrument is that you can sublty adjust the exact position of you finger, either to change the temperament, or for 'expressive intonation'.)

i am surprised about putting down several fingers at once; with the cello's longer strings, doesn't this make the 4th finger stretch uncomfortable? or is this why cellists shift so much?

btw, the cello part of Canon in D is the one where the cellist usually falls asleep, right?

There isn't a 4th finger stretch on cello. The cello is fingered 1 where the violin 1st finger would go, 2 for a semitone above that (low 2nd finger on violin), 3 where the 2nd finger would go on violin (another semitone higher) and then 4 where the 3rd finger would go on the violin (i.e. another semitone). You have to put all the fingers down up to the one that's fingering the note (i.e. if you want to play a note that's determined by your 3rd finger then you also put the 1st and 2nd fingers down in position) because the strings are a lot thicker and harder to depress.

Having originally done cello, I keep forgetting to take my lower fingers off on the violin.

That's not a bad thing though especially when you're only a beginner

But you've forgotten about finger extensions. If you are playing D major for example, you'd start on the C string with first finger for D, then you'd extend the second for E natural and then extend the fourth for an F#

My 'cello teacher, 40 years ago, was possibly somewhat unorthodox in what she taught me, and after the basic fingering in first position, with semitones between the fingers, she soon taught me extensions, with a tone between 1 and 2, then semitones to 3 and 4. You need this to play major scales without using open strings. Next came double extensions, with a perfect fourth from first to fourth finger, which I could do in first position: my stretch is fairly large, but someone with smaller hands would be able to do this in a higher position, where the distances between notes are less. If you can do this, you can also stretch an octave across adjacent strings - very useful.

I don't recall what she said about keeping all fingers down below the effective one, but I don't even do that on bass: the strings are thicker than on a violin but they are also longer and if you play enough, your fingers get stronger. I don't recall ever having fatigue in my left hand while playing bass, but my right thumb can give up on a long, loud, busy passage, of which we have several in Beethoven 7.

Finger independence is essential on all string instruments. While a fundamental hand position should be kept, even while the fingers are above the strings (so that the hand is prepared), keeping all fingers down all of the time is a very inefficient way of playing.