At the top of the GOP is the National Committee headed by the Chairperson. Each state has 3 members on the national committee – an elected committeeman, an elected committeewoman, plus the state GOP chairman.
At the state level organization varies, but usually there is a state committee, a district committee, a county committee, and the local precinct committee-person. There are currently thousands of precinct positions unfilled.
Dan Schultz of Arizona has created Project Precinct that explains how we can take control of the Republican Party by becoming precinct committeemen – The Neighborhood Precinct Committeeman Strategy to Take Back the Republican Party and then America at the Ballot Box. Dan says of 4,000 slots for precinct committeemen, about 2,000 are vacant. Visit his site for more information.