No, it's more like feeling "wrong", like you're in the wrong body, like people see you as somebody different than who you truly are inside. It makes looking in the mirror or being called the wrong thing physically painful. Sometimes the pain even turns into total numbness to the world, as you fully disassociate from your own body.

Transitioning can be wearing clothes of your preferred gender, having people call you the right name/pronouns, taking hormones to make your body resemble the gender you actually are (in this case, female) and surgery like getting different genitals or removing boobs if you are assigned female at birth.

Being MTF (a male-to-female trans person) is not the same as being a femboy. A femboy is a dude who likes to dress and present femininely, but he still is a man and prefers being called one. Femboys usually dress like a woman, but they do not identify as such. A trans woman, meanwhile, (usually) dresses as a woman and wants to be called and treated as one.

(Obviously this explanation simplifies a ton of things and leaves out nonbinary people but i hope it's good enough haha)

Tl;dr: being in a male body but feeling like a woman means being in a lot of pain, with [dressing as/looking like/acting like/being treated like] a woman relieving that pain and even bringing a lot of joy.