A great place to start is over at coinmarketcap.com where you will see all the cryptocurrencies available to buy, plus all information related to them; Current price (FIAT), Circulating and Max supply, Exchanges it can be bought on, Websites, and Charts.
Once you know which cryptocurrency you'd like to own you need to find out which exchanges it is sold on.
Bitcoin is the most accessible crypto and will be found on the majority of crypto exchanges, like Kraken, and Coinbase. For lesser know/more unpopular coins you might want to click on the 'Exchanges' tab on CoinMarketCap to see where they're being sold.
Some exchanges will require KYC (Know Your Customer) details from you. This may include personal information like Passports/Driving license etc.
Important! I can not advise you which exchanges to use. Please do your own research. And only use a trusted site!
Once you've passed KYC and have been accepted it is time to fund your account. You will need to deposit money from your bank account to your exchange account. FYI, this can take several days depending on which exchange you are using, and how you are sending your money.
Once your money has shown up in your new exchange account it's time to make an order.
There are a few different ways to do this, but for simplicity we'll only look at Market orders and Limit orders.
Market orders are buying the asset at the current market price. So if Bitcoin was valued at $10,000 and you wanted to buy 1 Bitcoin right now, you'd make a Market order and pay $10,000 for your 1 Bitcoin.
Limit orders are buying the asset at a set price that you want/hope to buy it at. So, if Bitcoin was $10,000 but you wanted to only pay $8,500, then you can make a limit order of $8,500 and hope the market value drops to your limit order. This could take minutes/hours/days/years, or never happen. Or alternatively, the market price may drop past your limit order, in which case you get the best price - Limit orders mean you purchase or sell a security at a specified price or better.
To sell your crypto it's basically the reverse of buying.
Have your crypto on an exchange. Set the sell order, Market or Limit. Collect your cash (FIAT) once completed, and withdraw to your bank account/order more crypto!
As well as exchanges there are other options for buying and selling crypto, but please, always do your own research before making a purchase!!
Sites like eBay allow users to buy and sell digital currencies.
You can buy Peer-2-Peer on sites like Bittylicious and Cryptomate (UK and EU only).
And there are OTC (Over The Counter) options and Bitcoin ATM's to be found IRL (In Real Life) too!
>Make it safe and send it to your own WALLET