What Are The Uses And Side Effects Of Prednisone 20 Mg?

Hi, now I m not looking for a moral or legal lesson here. So I got torn up pretty good from longboarding. My brother gave me a pill and told me to take it. I found out it was 20mg of prednisone. I ve never heard of this before and am not really sure about it. Legality aside, is this relatively safe to take? What sort of effects will it have? And is it safe to use along with Advil and/or marijuana?