first of all, make sure you don't buy "babydogeETH" by mistake. it's not the same, and it's a scam coin. twitter suspended that account https://twitter.com/BabyDogeETH
it's not on coinbase or any other exchange (that i know of) so you can purchase it by following these steps, using a google chrome browser on a desktop computer:
4. buy some BNB. it's only available at binance or binance.us -- this is the "funding source" for baby doge coin. so if you want $500 of baby doge coin you'll need that much BNB.
5. send it to your "binance chain" wallet.
6. send the BNB from the "binance chain" wallet to the "metamask binance smart chain network" side of your metamask wallet.
in metamask, scroll to the bottom of the assets tab, choose "import tokens" and use the correct "contract number" to create the custom token in your wallet. it's in the upper left of this page, where it says "contracts" and "binance smart chain":
copy the number from coinmarketcap's site, then in metamask, paste the number into the top field and all other fields will populate. then click "add token".
next, you'll want that same contract number handy on pancakeswap, to paste into the currency window, since baby doge is a custom token on their site.
if you ever get stuck and need a hand, most of us at the "saloon" have done this process and can help you through it. i'm sure some of them use a mobile phone, so they'd be able to help with that workflow.
don't be intimidated. :-) it's really worth it to create a wallet and be able to operate outside the big exchanges. and once you know how, it's really easy.