I believe if the Creator USER is noted on the record there can be a restriction to limit only to those records created. And a higher level can see all. For the type of databases I develop that restriction is not ever needed. But I did read up about it, just in case.
If you Google the search it will come up.
See "Editing record access privileges" in FileMaker Help and check out this particular sub section: "Entering a formula for limiting access on a record-by-record basis" for a description of how to set this up.