Rather is used for choices. Too is used to add or include something.
Would you rather pet kittens or watch a movie?
I want to pet kittens and watch a movie too.
Would you rather work or play golf?
I'd rather golf, but I have to work.
We are are going to movies.
I want to go too!
Too is also used as an adjective to show excess. The coffee is too hot to drink.
It's too cold outside, I need a coat too.
(The cold is excessive, so I also need a coat )
Rather is also sometimes used help describe things. The coffee is rather hot, but it won't burn your tongue. In this case rather means "to a certain extent", to some degree
The coffee is somewhat hot, but not enough to burn you.
Hope this helps!