The Houston Chronical has a guide to Texas' electoral two-step.
The caucus — officially dubbed a "precinct convention" — begins at 7:15 p.m. or when the polls close, whichever is later.[Posted by Amy]
Caucus-goers arrive and put their names and presidential preference on the "sign-in sheet." Ideally, they should show proof of having voted in the Democratic primary, but it is not absolutely necessary, according to the Harris County Democratic Party.
The group first elects a chair and secretary. Those two then take a count, noting the total number of people and how many are for Obama or Clinton. Delegates then are distributed proportionally.
For example, say 100 people show up at a given precinct on Tuesday night. If 75 of them support Clinton, and 25 support Obama, then she gets 75 percent of the delegates and he gets 25 percent. If the precinct has 20 delegates to allot, Clinton gets 15, Obama 5.