You can access the CSGO withdrawal page here. There, you'll see items being listed on the site by other users.
You can adjust the items you see based on various factors here on the right-hand side here:
Once you find an item you want to withdraw, simply click on it and further instructions will be given in the pending trades tab. Depending on whether the item is an auction or not, you may need to make an offer on the item, or you may be able to withdraw it instantly. All the on-screen prompts are very easy to follow, though!
To help you find items that are likely to be sent quickly, we have an indicator to show if the seller is online or offline. This is visible on the item card:
Online = activity on the site in the last 10 minutes or the seller is using a bot to list items
Offline = no activity on the site in the last 10 minutes
Make sure to keep an eye on the seller info shown too if you want to ensure you're receiving items quickly!
Once a trade has been initiated, you just need to keep an eye on your incoming trades on Steam for the other user to send you the item. Once you've received the item, the trade will be completed on the site and your coins will be deducted.