First you must realise breasts are not smooth, but a little lumpy. That’s the normal structure.
Iif you find one dominant lump it’s a different story. Dominant lumps are almost never subtle. They are normally the size of a grape.
The lump will stick out prominently among the smaller lumps that constitute normal lumpiness. It’s really something different.
If you feel one don’t panic: most breast lumps are benign. In pre-menopausal women only 1 in 12 lumps is malignant. But if anything is wrong, it’s important you seek help quickly.
If you find a dominant lump and it doesn’t disappear within two menstrual cycles, you should visit your GP to have it checked out.