To find out if a store has parts from your wanted lists, click Wanted List from the top navigation bar. This will show everything the store has from all your wanted lists; to check a specific one, choose it from the left sidebar. If a store has nothing from a specific wanted list, the list will be faded out.
The categories on the left hand side are split into multiple sections including: sets, parts, minifigures, instructions, and also colour. Clicking on any of these will show you all parts in the selected category; if you’re looking to make up your order so it reaches the minimum order quantity, this is a great way to find some random parts to buy (I generally buy some extra minifigure parts in my orders). This is also useful if you know what kind of parts you want to buy; choose the category, and check out everything the seller has.
Before checking out, click on the Terms tab at the top of that page; this page outlines any rules about ordering the seller might have, as well as an estimate of how long an order might take to process. The Store Terms usually shows which countries the seller ships to, estimated shipping costs, and minimum order details. For some stores, the terms and splash page are identical. It should be noted that not all stores will list shipping costs here, but most sellers will tell you if you contact them. If you are not happy with the rules outlined here either contact the seller to see if better terms can be negotiated, or choose another seller.
When you’re happy with the items in your shopping cart, click Checkout from the basket. On this page, review the store terms, choose a payment method, and choose a shipping address. You can also add notes to the seller.
Next: Read How Bricklink Works to understand what happens once an order has been placed.