The Committee is the executive body of OULD and puts on events every term for the membership. They are elected by the membership at the end of every term to serve in the following term.
The Committee is divided into three different sections, each with different areas of responsibility: Committee with Portfolio, General Committee, and the Appointed Officers. You can find out what roles there are, what they entail, and who currently holds it below - if there's a vacant position you might even be able to fill it!
Appointed Officers differ from other members of the Committee in that they are not elected, but rather appointed at the discretion of the President in consultation with the Committee. Many of their jobs will be more ad hoc and advisory in comparison to other portfolios.
You can read more about the general functioning of the society in the society's Constitution here.