How i know that, is i have breast tissue or just fat ? (having man boobs)

Probably both: In all likelihood, your male breasts are a combination of breast tissue and fat. You did not give your height and weight so it is difficult to determine.

Difficult: Similar palpating texture. Multivitamin surbex in moderate dose should have no major effect even with overdose. But you probably do not need. Lose weight.

See Plastic surgeon: Not enough information. If you are normal weight then see a plastic surgeon for an evaluation. You may need a full check up including hormonal levels and mammogram and then can be considered for surgical management by either liposuction or excision. If you are over weight then you will need to lose weight as some fatty breasts may settle.