Tutorial added : square threads in a simple way.
Select a plane similar to the plane shown in the image. It must be normal to the lateral surface area.
Sketch a vertical line as shown and exit the sketch.
Select the same plane again and sketch your required dimension square on it and then exit the sketch.
Select "swept cut" from the features menu.
Select the square as profile and the vertical line as the path. Set twist type to "twist along path". Set define by "turns". Select the required no. of turns. If the preview is according to your expectation, then select ok.
Here's your acme thread. Note that there are many ways to create an acme thread. It's one of them and a simple one as well. You can ask for tutorials based on helix also.