Sports teams do exactly what the name says on the tin.
Committees are student groups that are governed and elected by the JCR Meeting. Each Committee may have many internal positions but each committee must only have a single head.
There are two types of committee, Closed and Open. An Open Committee is one which anyone may join without interview or barrier. A Closed Committee is one that requires its members to be successful at interview.
Societies are student groups that are self-governing and self-elected. Each society has its own constitution and holds annual elections at an Annual General Meeting for key executive positions. Societies are more independant from the JCR than Committees.
Society constitutions can be viewed in the appendices to the Junior Common Room constitution for more information on the governance of each.