Here is a quick guide if you dont want to backup your entire website you can just backup (zip) these files and folders and DB values and you should be able to restore your site easily. 

Save all these items together in a folder on your PC.  Zip them up and download them to your PC in same folder.

1. Export your database - all of it. 

2. (zip) your ow_includes folder (you really only need the config but might as well do the whole thing its easier). 

3. (zip)ow_userfiles

4. (zip) any custom folders you have in the root. Some plugins create special folders in the root, youll know it if they do because you have dealt with them before im sure.  

5. Make a copy of your init.php and/or htaccess file and save it. 

That should be all you need to restore your site.  Everything else can be replaced with a new install of Oxwall and Plugins. 

Hope that helps... 

Dave :)