Uhm, I can't make a video to help you but I'll try to explain! :)
So, first do to the store, you can find it right here:
https://store.cubecraft.net/category/60093
Step 2: Type in your Username. ( The username that you use in Minecraft )
Step 3: Than, choose the rank you want to buy, scroll down and there will be a blue button saying: [Buy] Lifetime click on that.
Step 4: Click ''Add To Card''
Step 5: Fill in your full name, for example, Minecrafter Van De Hood.
Step 6: Fill in YOUR email addres, etc.
Fill in all the boxes, than, click on ''Contune to Payment''
Step 7: Purchase!
( There will be an email send, this email confirms that they have received your payment and you should receive your items soon. )
I hope I helped you! :)