Select the Wikipedia version you want to download and wait for it to finish. That said, first make sure you have enough free space on your hard drive (the Spanish version takes up 850 megabytes, the English version 5585 megabytes, the French version 1360 megabytes, and the German version 1779 megabytes).
Kiwix is a simple application that lets you browse Wikipedia offline, and includes features like advanced search and search history. The progress bar that indicates your download status will appear on the top left side of the screen, just below the word Corpus. You can also download more than one version of Wikipedia simultaneously. Just make sure you have enough free space on your device.