Unlock the portal and don't fall off! Use Arrow Keys or WASD to slide. You'll slide until you hit a black box. Grab the black key to unlock the portal, then slide into it to complete the level. When you move, the tiles you slide over will disappear, so think carefully about each move!

You'll also come across different colored tiles to slide on. You can slide on red tiles, which will then change to white and can be slid across again! Once you slide on yellow tiles, they will transform into black tiles that can no longer be slid on. Some tiles will have green boxes that will stop you from sliding.