First you need to make an account. Sign-Up here to start with $45 worth of coupons.
Then you need a link to the item you want to buy, beginners should look for Taobao and Weidian items.
You take that link and paste it in the search field on the Wegobuy homepage.
On the product page you have to choose the size and color.
Then you can either buy directly (buy now) or add to cart to buy together with more items.