In general, Monero is acquired through an exchange with another crypto, such as Bitcoin, and, more rarely, by purchase on a specialized platform. 

 If you don't know a platform, a Google search (or one on any other search engine), such as typing "exchange Monero (your country)”, or "purchase Monero [your country]" will give you many results. 
Carefully check, before any payment, the age and seriousness of the platform

Once you have chosen the platform, you will, most of the time, need to register in advance and then exchange or buy and pay (usually by bank transfer, or possibly credit/debit card. By paying by credit/debit card, you will get your cryptos immediately). 
Once the Moneros have been obtained, they will be stored on the platform on which you have procured them or in an online wallet of your own — or you can transfer them to a wallet that you have previously created on your computer/smartphone.
Then you can transfer all or part of it as you wish, in particular to make your first deposit on Atrad.io. 

We strongly recommend that you learn about cryptos with Bitcoins; then, if you wish, you can easily discover and use others like Monero.

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