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You need to "slice" the files, that is preparing them using a software like Cura (it's free) to arrange them over the printing surface while adjusting layer height, infill rate, speed (use the details provided by the creeator) etc., and then create a .gcode file to put on the microsd. There are multiple tutorials for Cura on YouTube and it also has a default Ender 3 profile, so it won't take too much time to start printing