I am trying to find out information about me and my sister's adoption . We were adopted in the 90's but I can't seem to find out how to get information on this topic.

I'm not an expert but I think it depends how old you are. If you are under 18 you have to have your legal guardians permission to view your adoption files.
Also it depends whether it was a closed or open adoption. A closed adoption is where the legal parents do not know anything about birth parents and vice versa. Open adoption is the opposite.
I don't know how you'd find what you want to find, but I do know that these two things will dictate how much information you will be able to have when you get there.

How old are you and your sister?

If you were born before today's date, 1992, we can't help you. It is illegal to help a minor search.

What do your adoptive parents say?

Most adoptions in the 90s were open adoptions--why was yours closed?

I am in the excat same situation. Most people can't help because of laws. So id would just keep looking

Actually, I'd talk to your adoptive parents. If they know you want to know, they may help as much as they can--and since they represent you legally, they can help you search.