Wait until the terrain loads and then you will have a playable character! Use arrow keys to move, space or up key to jump, click and wait to break blocks and to build tap on a block in your inventory and then move your cursor to a place you want to build and then press B. You get blocks by destroying them around you, besides leaves which turn to saplings.
Thanks to @FalconsFury for the game I just changed some stuff! (Different Graphics) V1.1. You don't go through blocks anymore :)