You probably received the charge of "Trespassing" along with a shoplifting charge because you were previously caught shoplifting at that same store and were told that you were not allowed to enter that store (or any store in the entire chain of stores) in the future. If you were previously caught shoplifting in a Schnuck's grocery store, for example, which is 1 of a chain of hundreds of Schnucks' grocery stores, it is common for the store to tell you that you are not allowed to shop or enter any Schnuck's grocery store for 1 year, or sometimes forever. So, if you did not realize that you were prohibited from entering any Schnuck's grocery store (not just the one you were caught shoplifting in), and you entered a Schnuck's store, then you violated the prohibition and you can receive a ticket for trespassing.
You need to hire a criminal defense attorney to represent you in court. The attorney may be able to negotiate a plea bargain with the prosecuting attorney to get the shoplifting and trespassing charges reduced to lesser offenses and keep them off your permanent criminal record. This is more difficult to do if you have previous convictions for shoplifting.