how to repair a stl file

there are many ways to repair a stl file.
in Rhino these ways are grouped in four categories which are: display, remove unwanted details, display and close gaps and offset. Many times when you need to offset a piece so you have a solid part and not a surface parts of the piece will be double and to use that file in the z print will turn to a mistake so you need to check and repair your file before you send it to print. to accelerate the process.
some things are going to be more complex than others. to me its easier to close a gap for example than to do a offset without repeating faces.