Jimmy — What makes a chord a minor is that you flat the 3rd ‚ i.e., instead of playing G, B, D, the G-major, you play G, Bb, D and for Am you play A, C (instead of C#) E.

Presuming y ou're talking about guitar, the Gm is most easily played by barring an Em up three frets. Lay your index finger across all six strings at the 3rd fret and the 5th and 4th strings at the 5th fret.

The Am is easier — just 2nd string, first fret and 3rd and 4th strings, 2nd fret. Only play five strings unless you want an alternating bass E (which rarely sounds very good in this configuration) below your bass note.

cheers,

david