Questions about authentication process

[slipk1068]

I have a pretty cool single signed baseball that I am considering getting graded, but I I know nothing about how the process works because I am mostly a card guy. I am slowly selling off a lot of my autographs, but I am hesitant to sell this one because I think it will bring more money if it is graded. I tried to figure out the PSA order form, but that didn't make too much sense to me and what I did understand, left me with a few unanswered questions.

1) It seems like grading and authentication are 2 different things?

2) Are they going to put a sticker, invisible mark, or deface my ball in any way and if so, is there somewhat respected company that wont deface my ball?

3) How do LOA's work? I have seen LOA's that are generic. They read something like "Clayton Kershaw single signed baseball in Blue Ballpoint pen" That seems to me to be easy for a scammer to swap out with a bogus ball, so maybe some kind of invisible marking is necessary. I just just hate the thought of defacing a ball, but maybe this is accepted in autographs more so than it would be in cards?

Thank you in advance for any help.