On ArcGIS 10.2, when I create a polygon from a point file, Why does it only draw a line for three sides, and how can I fix that?
Your question refers to creating a polygon from points, however as you state in your comment you're using the point to line tool. You then need to convert that line to a polygon using the Feature to Polygon tool. If your point file is simple, such as near a square, you can just use the Minimum Bounding Geometry tool to skip the point to line step
As it shows in the documentation for Points to Line the points input will be connected by a line. It sounds like you're looking for a closed geometry, which will require an additional step of Feature to Geometry according to this answered question ...it does look like you'll need an additional line to close it off though