There are different kinds of throw pillow covers, there are zippered covers, and buttoned covers, but easiest of all there is the envelope cover. The great thing about the envelope cover is that it looks as good as the other types of covers but is easier to make.
Here is a very simple tutorial I found that will walk you through making an envelope throw pillow cover step by step. It is very informative and easy to understand.
If you don’t want to use a sewing machine, don’t have one, or don’t know how to you can sew an envelope throw pillow cover by hand. Do exactly what the tutorial says, but instead of using a sewing machine in the sewing steps, sew everything by hand. Unless you are a SUPER fast sewing expert, sewing by hand will take longer than with a machine, but you’ll still get a nice product.