I am trying to become my fionca's gardian. what do I have to do.

Because you are asking this question under the topic "Social Security Disability" I will assume your fiance needs someone to handle her money.  Instead of guardian, the Social Security Administration  (SSA) refers to such  a person as a representative payee instead of guardian. There are a series of steps that are required.  You can learn all about the process at the website of SSA http://www.ssa.gov/payee/index.htm