Wait 5-10 seconds for it to load. Use Up/Down arrow keys to change your block. Press I for information about your current block. Drag the red and yellow circle to set the spawnpoint. Click the thing at the bottom to open the menu, where you can switch to play mode, change your character, set the jump height, save a level, and load a level. Click the top of the menu to close it. Post your level codes in the comments.
Coding 100% by me. Physics by me with lots of tutorials. Logo by flamingtext, some of the characters are from scratch, and all other art by me. Music from Megaman 3.