The easiest way to get BNB is to go directly through Metamask.
Once you are logged into your wallet, click directly on "Buy":
Then select "Buy BNB with Transak":
Select the amount of BNB you want to buy (we also recommend you to buy via CB to get your BNB quickly) and then click on "Buy Now" (the transaction fees of the Binance Smart Chain are very low, usually a few cents so 30 euros are enough for several hundred transactions)
That's it! You will receive your BNB within 4 minutes directly on your Metamask.