The Church has a new system designed to use just one username and password to log onto Church software systems. You are already using this single username and password if you currently use your stake or ward website.
FamilySearch is using this single username and password for the Research Wiki. New FamilySearch and FamilySearch Indexing will begin using the single username and password in the near future.
It would be a good idea to obtain a single username and password now rather than waiting for these family history applications to begin using it. You can go to ldsaccount.lds.org and obtain what is called an LDS Account. You can also check to see if you already have an account or you can use the links on the page to remind you what your username and password is if you have forgotten them.