So you are coming here to learn how to pay for a little piece of plastic with some ink on it. You have a couple of options technically but really just use bitcoin. You will be much happier and your IDs will come quicker.
1. Go get a bitcoin wallet, I use blockchain but it's just personal preference, they all have there own pluses and minuses. This separate wallet is so your bitcoin buying account doesn't get banned or blocked because you are buying something illegal remember. So go get a separate bitcoin wallet and make sure to have a couple extra dollars for fees.
2. Buying bitcoin
Option 1: Coinbase- Here is a guide cause I am lazy. https://www.coinbase.com/buy-bitcoin
Option 2: Localbitcoins- So this is a good option and works well if you are in a populated area. https://localbitcoins.com/guides/how-to-buy-bitcoins
Option 3- Paxful: If you have some gift cards laying around or want to use PayPal Paxful is your go to. Buying off Paxful depends on the vendor so you will have to learn for yourself.
Option 4- Bitcoin ATM- It's like it sounds, you put money in and get bitcoins into your account. https://coinatmradar.com/ That site will be very helpful for all bitcoin ATM stuff you will need.
3. Sending bitcoin
So you bought your bitcoins and now you need to send it to your wallet. Here is the link for sending off Coinbase. You will need to find your wallet address and this depends on your wallet so just go google it if you can't find it.
Now you want to send it to the vendor. The vendor will give a address and depending on vendor a QR code with all the info needed. You either copy and paste the address or scan the QR code and send the money to the vendor. I always send $1-3 dollars extra just incase fees or the price of bitcoin fluctuates a huge amount in the time its transferring. Some might go and ask for a transaction hash and again this depends on the wallet so go google where to find it.