Found it from the FAQ section.
What is a congressional district caucus?
State Convention delegates will meet twice in caucuses made up of only those from each of the state's thirty-six congressional districts.
Delegates there will elect a permanent caucus chairman, elect three delegates and three alternates to the Republican National Convention, and elect one person to the National Nominations Committee. Delegates will also cast votes for the positions of Presidential Elector, National Committeeman and National Committeewoman. For these positions, the recommendation of the caucus will be forwarded to the National Nominations Committee by the district's member to the committee who shall support them on at least the first round of voting
http://convention.texasgop.org/faq