Hi! I have made some adjustments to be a bit more grammatically correct, although, as natives, we often shorten sentences and some of your shortened versions would be acceptable: FIRST TEXT: I gave you  a text in the last lesson, remember? Yeah, I do. Well then, tell us about it/talk about it standing at the front of the class/standing next to the blackboard. You may also do it sitting down where you are. > I've clarified "standing next to" the blackboard, as when you only use "by" it can be a bit confusing for non-natives - whether you mean "standing by the blackboard" or "using the blackboard to explain". NEXT TEXT: We painted the container on the back of the car (this means that the container was painted while physically on the back of a car - like a pickup truck). We painted the container at the back of the car (this means that the container was painted while on the ground near the back of the car) My brother loosened the bolts, replacing them with new ones, and then I tightened them. > I changed the order of this sentence to be chronological, it is confusing to say that you loosened them, then tightened them, and then replaced them. I hope this helps!