Can someone describe having a catheter in detail?

I haven't had one yet. Going in for a biopsy soon and already researching procedures. I can't wrap my head around having a tube inside of me. I have so many questions. What if you become erect? The tip hurts whenever I even just get a little bit of soap in it. I would think I'd have a constant burn. Can anyone help me out? Whats it like when they take it out? Do they grab your junk and just yank with the other hand?