user_id

I have several tables I am using.   One is a user table another is education table.  The problem I have now is getting the user_id to be inserted into other tables.  I found a posting closed to my situation about using sessions to get the user_id, but am still having problems.  I have tried to use the simple recordset to get the user_id by selecting id and using session variables and mm_username as a filter.  Nothing is coming up can someone help me?