Breast cancer?

Ok so I've never really been taught about breast cancer properly, so whenever I try to feel for lumps in my breasts I'm not really sure if what I'm feeling is nesesarily normal? 
I'm a 34DDD and when I feel myself up there are like solid masses but I'm not Really sure if they're something to be worried about? It's very hard to describe, I'm not really sure what is considered "normal" on the standards of feeling
I'm only 17, and so I know the likelyness of me getting breast cancer now is unlikely (i believe) but I do have a lot of cancer that runs through the family and would like to know what I should look for in myself in case I ever feel like I really am having an issue.
Any help helps! Thank you!