Open the desired archive in Entropy and click on the extract button in the toolbar. Select the location where you want to extract the files and click on "Extract".
Open the archive and select the files that you wish to extract. Then drag them to their destination.
Alternatively, you can press down on the arrow next to the extract button in the toolbar and click on the "Extract Selected" option.
To automatically extract and open a file from an archive, simply double-click on the desired file.
By default, opening an archive with Entropy displays its contents. However, you can modify this behavior in Entropy's preferences so that archives are automatically extracted when opened, similar to Mac OS X's archive utility.