Em: the first shape
Fret the A and D strings at fret 2 with two fingers. Strum all six strings. Test them one by one; if a string is muted, move your fingertip a little closer behind the fret.
Am: a different sound
Start your strum on the A string. Fret D and G at fret 2 and B at fret 1; leave out the low E. Change slowly between Em and Am and hear the difference. Find interactive shapes in the chord dictionary.
Why does my chord sound muffled?
A finger may be touching a neighbouring string. Curve your fingertips and test each string on its own.