Portal is a game were you use portals (der) to plat through 19+boss levels and this game is very tricky. You need to think real hard so if you think you can't think real hard only play levels 1-9. Otherwise have fun.
In the game you will find out at about level 10 that there's a cake running gag. In the end it will show you the cake. If you want to know
how to beat the boss click the link>/cheats.html.