The Electronic Comment Filing System is the database that houses FCC docketed proceedings from 1992 to the present. There are selected pre-1992 proceeding documents available in the ECFS, as well.
The official records of FCC proceedings are published in the FCC Record.
The FCC's user guide for ECFS is available here.
There are two primary methods to search for documents in the ECFS database, either the unique number assigned to a document or docket or through a keyword/full text search. See the sub-sections, listed in the left-side menu, for more information on each.