Mobile App
1 - Tap 
at the bottom of your screen
2 - Tap 
to expand the field and enter the $250 as the amount
3 - Tap From and choose "Bitcoin" from My funds
4 - Tap To and choose "Nano"
5 - Tap 
6 - Tap 
7 - You're done!
New Web Wallet
1 - At the right, at the Transact Panel click to expand the field and enter the $250 as the amount
2 - Click From and choose "Bitcoin" from My account
3 - Click To and choose "Nano"
4 - Click
5 - Click
6 - You're done!