Now that you have searched and found the Xena Store them from the search bar.Once you see that them, Under it , you are going to see install, preview and details. You are going to click install. I cant you the Xena Store theme to show you, so I will use a different theme to show you.

Im just using the first theme as an example. once click on install, youre going to see a page where it shows that its downloading and installing the theme.

Once its done you can click activate. Im not going to click on activate but, it will take you to a page where you can customize your theme.

After you have customized your theme, make sure you save it. After that you can go and add whatever you want to add on to your site. Now I didn't create an online store, but this is how you create it using word press. If you need any more help please use the comment box.