You can check your balance by clicking on your profile photo in the top menu bar and then clicking on "Wallet". This page will show you how much your account is worth with your combined Steem, SteemPower and Steem Dollars.
To withdraw you will need to transfer your currency to an exchange and the decide what you want to do from there. There are plenty of guides on how to transfer funds if you search :)
Here's a guide on how to transfer/withdraw that I found for you
https://steemit.com/steemit/@dojoexle/step-by-step-how-to-cash-out-your-steemit-earnings-to-usd
Thanks dude. You helped a lot.
Very helpful. I do research about this now