After you get some bitcoin, I would probably split up and buy from tradeogre and southxchange.
I generally use coinmarketcap (CMC) https://coinmarketcap.com/currencies/denarius-dnr/#markets
to look at prices between the different markets. Generally the BTC/D trading pair will be the one to use, especially for someone new right now.
Click the D/BTC and it will take you directly to the order book. You will want to register on each exchange, with a strong password and use 2FA like Google Authenticator or Authy. Google Auth basically works on the phone, and Authy can be used on phone, tablets and PC.
The account is almost instant to setup. Then you go into your wallets and deposit BTC into your BTC wallet address. That will take about 30-60min as bitcoin is very slow to move from your own wallet to the exchange wallet. Once the confirmations are complete, you can then buy D using the BTC that was sent in.
If you have any questions, click the discord link in my signature and myself or probably lots of people can help you with any more questions. Discord is full of scammers, so generally be cautious about people private messaging you on there.