1
She plays the flute in the school band.
To sign this, you would point to indicate 'she,' then sign 'flute,' and 'school band.' Because the sign for 'flute' already looks like playing, you can often drop a separate sign for 'play' and just use the instrument sign to convey the action.
2
I want to learn the flute.
Start by pointing to yourself for 'I,' then sign 'want' and 'learn.' Finish with the sign for 'flute.' Keep your finger wiggling smooth and continuous to show the ongoing action of playing the instrument as you express your desire to learn.
3
The flute music is beautiful.
Sign 'flute,' 'music,' and then 'beautiful.' When signing 'beautiful,' make sure your facial expression matches the positive, pleasant meaning of the sentence. Your face should look relaxed and appreciative to complement the graceful wiggling motion of the flute sign.