Theft is a broad criminal charge in Texas that includes a range of offenses from shoplifting and larceny to bouncing checks to buying stolen property. The punishments generally depend on the value of the stolen item, and can be as little as a fine or as serious as prison time in extreme cases.
The Texas Penal Code defines theft as taking someone else's property without consent, either by deception or by physically stealing it. You don't have to keep the property for it to be considered theft, but only long enough to deprive the owner of its value. And, if you take something, then return it for a reward, that is also theft under Texas law.
To charge you with theft, the police need to show that you acted with criminal intent, meaning you knew the property belonged to someone else and knew you didn't have their permission to take it, and that you actually have or had possession of the property. They can do by that using physical evidence, such as security camera video in a shoplifting case, or by statements from a witness, an accomplice, or you.