This information is for 6 string guitars only, not 4,5,6,7,8,12, etc. stringed instruments.
If you're not sure that you own a 6 string because strings are missing, just count how many tuning pegs there are.
NOTE: Most guitarists refer to string #1 as the top string, even though
physically it is on the bottom.
We say this because, MUSICALLY it is higher in pitch.
For the same reason, the 6th string is the bottom string because its the lowest sounding string.
string 1 = high E (highest pitch, thinnest string, closest to ground) string 2 = B string 3 = G string 4 = D string 5 = A string 6 = low E (lowest pitch, thickest string, closest to ceiling)
The name of the string also represents what note it sounds. Ex. To play a B note, just play the 2nd string open.
1 If your guitar is electric or acoustic. This should be straight forward. If
unsure, bring your guitar in to the music store and they should know. ( I have
used electric strings on an acoustic, it wasn't as loud but had a softer touch )
1b Some acoustics (classical) use nylon strings. Know if your acoustic uses nylon or metal strings.
2 What the string number and name is.
3 What the string diameter is.
The string diameter of each string should be listed on an old pack of strings. If you don't have an old pack of strings, I recommend buying a whole new set (all 6 strings) and starting with a fresh new set on your guitar.
There are different gauges to buy, so if your unsure here's my recommendations (remember this is only my opinion - others may disagree)
For electrics try a pack with string #1 (high E) .009mm in diameter.
For Acoustics try .011mm as the high E string.
( the rest of the strings will follow accordingly )
Another name for the above sets of strings are electric 9's or acoustic 11's.
I choose these because they are a light gauge and easy on the fingers, but not too light that they'll bend out of tune easily. You'll get to know what you like in time - different guitars and different people need different strings.