How to tell if it's a breast cancer lump or some sort of other lump?

See physician: An experienced physician can often differentiate the lumpy-bumpy normal tissue from suspicious masses. Their exam, combined with your medical history, will guide them to ordering additional imaging and possible biopsy.

Breast lump: You need a clinical breat exam and either mammogram or ultrasound, maybe both. See a doctor/clinic.

Removal: The only sure way is to have the lump removed and the tissue examined by a pathologist.