A useful document has been compiled by three Attorneys from Houston, which sets out some of the basic information that inmates and their friends and families may need when an inmate is preparing to move from a county jail into a TDCJ prison.
The document is here
http://tifa.org/wp-content/uploads/2013/09/Going-to-Prison-in-Texas-Habern-2014.pdf vis the Texas Inmate Families Association website.
Some of the information I have read in the document is a generalisation, some not strictly accurate in all circumstances, particularly in the section that covers Security Precaution Designation. But there is some very good advice on "Doing your own time" in it and I think it is worth a read.