In general, cryptos like Bitcoins are purchased on a specialized platform; there are many of them.

The following site lists, depending on your country and payment method, the main platforms:
https://www.buybitcoinworldwide.com/

Otherwise, a Google search (or that on any other search engine), such as typing "buy bitcoin [your country]", will give you many results.
Carefully check, before any payment, the age and reliability of the platform.

Once you have registered with us, you can also ask us — via a ticket — about the platform choices available according to your country of residence.
Once you have chosen the platform, you will — most of the time — need to register in advance and then buy and pay (usually by bank transfer but possibly by credit/debit card. By paying by credit/debit card, you will get your cryptos immediately).
Once the bitcoins have been obtained, they will be stored on the platform where you purchased 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, especially to make your first deposit on Atrad.io.

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