To build with something, DOUBLE CLICK on it and drag. Drag it to the red X to delete it. You can also double click + drag blocks you've already built with to duplicate them.
I spent a long time on this. I hope you like it! Thanks to @andytphan @TheMysteriousPenguin and @Blackapple621 for helping me improve this! Updates: v0.0: nothing u derp v0.1: Added background and first row(the red X was there, but it wasn't functioning properly) v0.2: Added complicated, glitchy controls for building(it was the only way I knew how to do it) v0.3: Fixed building; added double click + drag v0.4: Fixed Red X v0.5: Added "Please read instructions before playing" text. v0.6: Made it so you had an unlimited supply of blocks. v0.6.5: Bug fixes.