Below you'll find a tutorial presented by William Varela on creating star trails. The instructions here will enable you to create star trail photographs using a completely free open source application which is available for download from the web.
The first video will walk you through the camera settings and the steps required to shoot the images that will be processed into a star trails photo.
The second video will show you how to set up and install the Startrails program which will merge your individual star images into a single star trails photo.
Finally, you can take a look at at short video above compiled with all the stills.
And thank you William for taking the time to put this all together!