If you look around hogwarths then you will find Lions with Crests (The lions are made of stone and crest a kind of statue) What you have to do is find some people that are arguing and click on them (or you can click the lion doesn't always work) and you do a duel (the people are weak) and if you win then the crest realizes from the lion and you win a crest
There are hidden crests in banners that hang down in the corridors. You have to run and touch A as you get to the banner for Harry to jump and hit it. Doing this will make another banner infront of you (or around the corner) drop down do the same with this (press A to jump and hit the banner)and another banner will drop down when you hit this one a crest will fall down. There are 3 separate places these crests are hidden on the banners.