So for Crypto Currency there are quite a few places if you google claiming to allow you to buy and sell crypto, but like everything we've covered before, there are scammers out there, so be careful.
Here are a couple of places I recommend as I have used them sucessfully without issue, have been around a long time and have site security;
Coinbase, the most well know and easiest way to buy and sell the main Cryptocurrencies. They even have an app you can use. Also they give you a bonus when you trade $100 / £7.
LocalBitcoin (great to get cash in bank)
I have used this service a few times now, and like it a lot. You can view the different traders and pick the best price that is on offer and start a trade. When buying or selling Bitcoin I have used the National Bank Transfer trading and it is great.
When buying you will start a trade and then be given a bank account to transfer funds to, once they receive the finds they release the Bitcoin into your LocalBitcoin account, and from there you can withdraw to your own Bitcoin account.
When selling Bitcoin you first need to deposit Bitcoin into your LocalBitcoin account and then you can start a trade to sell your Bitcoin, you give them your bank account to deposit to and when they have put the funds in your account you release the Bitcoin to them, its great. The Bitcoin is held in an Escrow service so it is safe and won’t get ripped off. I also have found the rates and fees to be great, I sometimes use this to fund my Coinbase
Bitfinex (proper exchange & trading platform)
I first used this to get some IOTA coins as this is the only place you could get some from, but it is a great platform. Has a full margin trading platform and exchange and you can also fund margin trades to get interest on your funds, although I did not find this very profitable.