The CAF is an organization that handle different social benefits, like the housing benefit (APL).
This application must be done as soon as possible: the estimation of your benefits starts on the day you apply.
The more you wait, the less you can get these benefits.
You can start this application before obtaining you residence permit card or your OFII stamp.
You will then have to complete your application to get the APL.
The application for the APL is to be made on the CAF website.
Then you must complete your application.