I was looking up who you could marry and I wanted to try and marry Ysolda. I found her but she won't say much to me. I haven't started the mammoth tusk quest because I'm not sure how to. Can't tell if I need to talk to someone else or what the issue is.

Probably someone else or glitch.

Could u kill the mammoth? i try to kill one but then comes 3 giants and 4 mammoths chasing me LOL

She doesn't say much, however the strategy guide states that once you do the quest for her, and you wear the appropriate amulet, more dialogue options will be available, and marrying her is then able.

I found the best way was to get up on some rocks or something, and take it out from a distance with either magic or a bow.

Try to go somewhere where the giant can't get to you, and shoot arrows until it dies. It's what I did =P And try to find a place where there's only 1 mammoth and 1 giant guarding it.

You have to wear the amulet of mara and, I think, do her quest.

Yes you can marry her (I did), you will probably need to do the mammoth quest first (which is what I did), then get the amulet. Best bet is to go to the tower that is not far outside the city were she is (forget the name) and go to the mammoth spot that is very close to it. Bait one to follow you and run (and keep baiting it), and try to take it down from the tower... do not try to fight it with the giants around.

I won't tell you how but you activate the marrying option in riften.

I just bought a Mammoth Tusk from the Khajit traders

You took the easy way out!

Wish I had known about that though...

Yeah I had to kill a two giants for that quest. I found the tusk on its body. A lot of hit and runs while fighting them.