Hi, and welcome to Particracy!
Cabinet ministers are mostly for RP, but some of them do have important roles, which you can access from the bottom of the Cabinet page (where it says "Ministers can perform their executive actions on this page.")
So the Head of Government can draft a world-wide press release, which will be visible in the
Global Gazette. The Foreign Minister can do that as well, in addition to being the one that can draft an international treaty. The player that controls the Foreign Ministry is also the one able to propose the ratification of an existing treaty (list of current treaties is
here). The Minister of Finance can propose a taxation bill and a spending bill.
Other than that the other Ministries are more of an RP tool, but a rather important one. In practice the Head of Government is the most important position, more so than the Head of State, unless the two are held by the same person in a presidential system.
Hope this helps!