Hi, I'm new to this too and cryptocurrency, VPN and TOR can be a pain at first. Get the Tor project browser and a VPN (Protonmail do a free one), then just look at reviews on the site to see what seems kosher and what to expect. Check postage details, some people say don't like tracked as if you check where it is that's another way to link you to the delivery (I don't know about that). Log in before buying, so that you have an order number and ability to raise a dispute and review service (I found a useful thread on this after doing it and it reassured me that the cash hadn't just disappeared).
For me buying Bitcoin in the first place is easy and safe with Coinbase but it is linked to you, so don't use that account if you don't want to be linked with a purchase. You can send BTC to an anonymous wallet (Electrum works for me) on your computer. I think this can still technically be traced back but some effort would have to go in, so if you're not dealing don't worry. You can use a mixing sevice to hide BTC origin if want real secrecy. Just remember each time you move the BTC around you're losing money in fees. If you don't want to use your bank account to buy your original BTC, you can use Paxful to buy Bitcoin anonymously, but the rates are worse, you can even arrange a meet up in person and exchange cash (doesn't sound very appealing to me). If you're in a big city there may be a bitcoin ATM near you, then you can exchange cash for BTC.