confused??

'fifth' is used usually to indicate an interval: two notes either played together or after each other. A fifth interval means playing a note and then playing the note seven semi-tones higher. Example: C-G, A-E, F-C. We call this the fifth because the second note is the fifth note of the first note's major scale (I know, horrible sentence).

Example: C-G. G is the 5th note of C-major: C D E F G A B.

C-C = unison
C-D = major second
C-E = major third
C-F = (perfect) fourth
C-G = perfect fifth <------------------ fifth interval
C-A = major sixth
C-B = major seventh
C-C2=octave

Now chord progressions are somewhat different, and you use Roman numerals for it. Let's stay in C-major, you get these diatonic chords:

I-C
ii-Dm
iii-Em
IV-F
V-G
vi-Am
vii-Bdim

A I IV V progression in C means a progression using C, F and G. I IV ii vii would be C-F-Dm-Bdim etc.

In other words, those roman numbers refer to the diatonic chords of the key you're in.

so u mean they refer to the chords that mach the key like in key of C C,C6,dm,em.etc

yes all the chords in a key are built completely notes in the scale, you can build every one by starting at a root and then just skipping a note and then skipping another one. For C major the I you build it with C (skip D) E (skip F) G so C E G makes a C chord. All the right chords will just naturally make themselves when you do this.

Here's a useful table:

Harmonising the major scale:
Degrees of notes C major scale notes
1 2 3 4 5 6 7 8 C D E F G A B C Chord no. Chord name.
-------------------------------------------------------------------------
1 3 5 C E G I C major
2 4 6 D F A ii D minor
3 5 7 E G B iii E minor
4 6 8 F A C IV F major
5 7 9 G B D V G major
6 8 10 A C E vi A minor
7 9 11 B D F vii° B diminished

Yeah you could also do a nice progreshion using the 2,3,and 6 scale dagrees.
by the way the names for these are
1(C)=tonic
2(D)=sub-tonic
3(E)=mediant
4(F)=Dominant
5(G)=Sub-dominant
6(A)=Sub-mediant(i think :oops: :?: )
7(B)=Leading note(again I think)
8(C)=tonic
9(S)=GIT SNAKE BIT