Launch GUI Tar and click on the Compressor tab if it is not already highlighted.

Add the files you wish to compress and/or archive by clicking the + button. You can select either one or multiple files at the same time from the Open panel. Files can also be added to the list by dragging and dropping a collection of files onto the Files table in the Compressor window.

Select the compression type: 7z, bz2, gz, tar, tbz, tgz, Z, or zip.

Click on the Compress button. If you chose to only compress the files (bz2, gz, or Z), the files will be individually compressed. If you archived your files (7z, tar, tbz, or tgz), a Save panel will drop down, prompting you to name the new archive, and where to save it.

Drag and drop a collection of files onto the GUI Tar icon. By default, GUI Tar will compress and archive the files as a tgz file if you have not run GUI Tar before. Otherwise, GUI Tar will remember your last compression type. Next, click the Compress button.

If the collection of files contains any compressed or achived files, GUI Tar will ask whether to compress or extract the files. Select Compress.