Tucking refers to the practice of tucking your penis and scrotum in such a way as to make them less visible. Tucking may be used by transgender folk to alleviate gender dysphoria, and can be done with compression underwear (known as a 'gaff') or with tape.
Some people never feel the need to examine or question the gender they were assigned at birth. But for many people, the gender they were assigned at birth doesn’t match how they feel on the inside. Gender dysphoria refers to that ‘misalignment’ between the gender a person feels or identifies as, and the one assigned to them at birth. So the goal of many ‘gender affirming’ products such as gaffs, is to alleviate that gender dysphoria.
And as always, listen to your body and stop if you experience any pain or discomfort.
Yes, tucking is generally safe. The main risk is skin irritation, so you should practice good hygiene and ensure you: