adi
The chords progression is C G Am F. I do not realize what notes to play for solo, is it only picking the cord on individual notes or I can play extra notes?
The notes in the current chord always sound “right”. Major and Minor chords are triads so that means 3 notes to choose from that belong to the chord.
But there are more notes you can play. The chord progression you posted is in C Major, so you can try using the full C Major scale:
https://en.wikipedia.org/wiki/C_majorSome notes in the C Major scale don't sound as satisfying as others across particular chords in the progression. They are called non-chord tones:
https://en.wikipedia.org/wiki/Nonchord_tonePlaying only chord tones limits melodies. It is more interesting to mix in non-chord tones too. Sometimes they are called “passing notes” because you play them as part of a movement to the next chord tone without staying on them for too long.
An easy scale for improvization is the Pentatonic scale:
https://en.wikipedia.org/wiki/Pentatonic_scaleIt only has 5 notes instead of 7 (like the Major scale) and sounds fine with all chords in the key. It's a popular scale because it is easy to play melodies that sound good. There are a lot of YouTube videos about Pentatonic scales.
By the way, this is the extent of my knowledge so please explore the links or YouTube. I probably can't answer deeper questions because my music theory is basic. I solo using a pentatonic scale and sometimes I use the full major scale if I'm feeling more brave
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Stefan