If you were to learn just a select few Meta-SQL, these are the ones that I would recommend:
%SelectAll
%SelectAllByKey & %SelectAllByKeyEffdt
%Table
%DateIn & %DateOut
%Insert
%Update
%Delete
There are many others. Please refer to the PeopleTools PeopleBook for more information.
Update 5/7 — Fixed the links to point to the most resent version of PeopleTools