Beginner's questions 2 - plant from internet

Hello! I am a beginner's beginner, I got a 90 gallon tank from my friend
and
want to set up a planted tank with lots of neons...(look like will be
pretty...)

I check around internet but got no inform on this one, should I pre-treat
the plant I am buying befor set them into tank? What kind of treat should I
put on them, wash them?

I put a thin layer of fertilizer (the red stuff from petsmart), and have
some small graval stone on top.

On the other hand, should I use tap water or what?

Thanks a lot!

Doreen