It depends how familiar you are with chords in general. A quick look through the syllabi for ABRSM jazz and I can't see any 7th chords/arpeggios, but there are some 9ths. However, let's stick with 7ths for now. I hope this doesn't confuse you!
Amanda pointing you to Pete's pages is a good start, but to elucidate a bit. Take G7. It' a chord using G as the root plus the 3rd and 5th notes above it, which forms a G triad: G,B,D. Then the 7th note is added. However it is not F# as you might think if you were thinking that G was the first, tonic, note of a scale. G,B,D,F# is in fact denoted GMajor7. What happens in G7 is that F natural is used. If you are still thinking in GMajor, you can consider the F# as flattened. So G7 is G,B,D,F.
7th chords like that (A7, D7, C7..) are known as dominant 7ths as they are built on the Vth or Dominant note of a scale. Thus G7 is built on the Vth note of C major, the notes in the chord thus being taken from C Major are G,B,D,F (natural). You can think of eg, C7 in the same way: C is the Vth note in F major, so the 1st (root), 3rd, 5th,7th notes are C,E,G,Bb. Dominant 7ths are used a lot in jazz and popular music.
It takes a while to get to understand these and other extended chords, but practice will get you there.
I hope that helps, not hinders!
Those chords will be the underlying ones that support the meolody, so yes, using the notes from them are a way to start with improvisation.
No, you don't just take the 7th note and flatten it. I was just describing how the 7 chord is derived and one way is to think of it is as having the 7th flattened against the major 7th chord. People who are starting with chords/arpeggios on single note instruments somtimes get confused between 7th and major 7th. You just have to get to know that G7 is G,B,D,F; C7 is C,E,G,Bb; D7 is D,F#,A,C; A7 is A,C#,E,F and so on. A useful resource for basic chords, even though it is for piano, is http://www.telacommunications.com/nutshell/music/index.htm
Hi Yc,ok thanks can take in the reply about chords giving a start to improvisation...But at moment cant get it in my head about the rest,i.e7th and major 7th,can see G7 as being G,B,D,F as you put it,but lost onC7,cant figure out where Bb flat came from!!! Think maybe give up on sax and stick to Martial Arts!! No i shall persevere. Thanks Dave.
First, sorry, I must correct an error. A7 is A,C#,E,G
If you've got G7, then look at C7 the same way. The C is the Vth note of Fmajor. Fmajor has one flat, Bb. If you take the root of the chord as the Vth, C, then the 3rd, 5th and 7th notes from there in Fmajor are E,G and Bb.
Another way to look at it, without I hope, confusing you further, is as follows:
In G7 again, the interval between G and B is two whole tones - a major third. That between B and D is a tone and a half (three semitones) - a minor third. That between D and F is also three semitones - another minor third.
You will find that same structure in all 7th chords - major third + minor third + minor third.
In major 7ths the final interval is two whole tones - a major third, so in Gmajor7 it would be D-F#.
I suspect martial arts have similar technicalities which is maybe why I have never tried!