I was trampolining and landed awkwardly on my foot. 10 Minutes late it started swelling and was bruised and I find it difficault to walk on it.

You've sprained it.

Here is a basic guide to help you with it:
How To Care For A Sprained Foot | LIVESTRONG.COM (http://www.livestrong.com/article/356152-how-to-care-for-a-sprained-foot/)