How to buy theme

Hello guys, I just want to know, how I buy Vantage theme, I haven’t have buy something online, like theme or plugin, so I just want to know how to do that, so I’ll not did something wrong, where if I did something wrong, and maybe my money not getting send to SiteOrigin, and my money loss… So please just quick little step, so I’m sure when I buy premium features I did it in the right way… Thanks :D