1. how do find what key is being played if your jamming to a backing track and you dont know the chords, and how do u find out if you do know the chords this is in relation to improvising solos over the top? like if it was 1 chord like an Am i would use an Am scale but if there are different chords being played how do u play along?

2. i hear alot about I, IV, III, etc chords or something like that and i havent got a clue wot thats about, could anyone explain, its when people say liek 'theyre using a pattern of I, II, V' or something along those lines i really havent a clue :S

any help would be greatly appreciated
1. whatever the first chord is usually defines the key. if it starts with an Am, the track is probably in Am. just jam in the A minor scale to it. if it changes chords, it doesnt matter, its still in Am. you dont have to change anything. a more detailed explanation, if you look at the A minor scale, you'll see way more than just the A minor chord, theres also C major, D minor, E minor, F major, etc etc. if you play these chords, as long as they're on the A minor scale, you're still in the key of A minor.

2. the roman numerals (I, II, III, IV, V, VI, VII) refer to the notes in a scale. in the case of, say, C major, that would mean I = C, II = D, III = E, IV = F, V = G, VI = A, VII = B. So saying the chord progression is I IV V, that would mean the chord progression is C, F, G. For different scales it gets more complicated though, because you have to deal with sharps and flats and stuff.
But if you plan on doing any shred solos, learn your modes...then you can just put in a piece
of shred whereever you want.
The key is basically the key signature of the song -- the number of sharps or
flats. In standard notation you see it marked on the left side of every bar line.

You can't always tell the key by the first chord. It all depends on the progression.
For example, a common progression, II-V-I, the key would be the last chord.

Roman Numerals. They are the degrees of the scale, and yeah they refer to the
notes -- 7 notes = 7 degrees. The reason to use that rather then letter names,
is because a letter implies a particular key. A number is independent of any key and
can be applied to all keys.

When talking about chord progressions, the degrees would refer to the harmonized
triads of the major scale. For each degree, it comes out either major, minor or
diminished triads as follows:

I Major
II Minor (generally written as ii)
III Minor (iii)
IV Major
V Major
VI Minor (vi)
VII Diminished

So a II-V-I progression in the key of C would imply

D minor - G Major - C Major

Hope that makes some sense.