Most instructions are inside the game itself. Click/Tap on Tom at the Leaky Cauldron to talk to him. On mobile, top on Tom and then quickly tap somewhere else or he will keep on saying 'Click to talk to Tom the Bartender.' To go to Diagon Alley click on the third brick above the dustbin.
This is for the Magical Mixes SDS studio. Thanks J.K. Rowling for creating Harry Potter. The sprites, backdrops and sounds are from the Scratch Library or the Internet. Considering the recent controversies, I do not support J.K. Rowling.