To buy Bitcoin as a beginner will be better through peer to peer transactions where you can just get the Bitcoin through any p2p platform be it centralized exchanges or decentralized exchanges. As a newbie if you have already learned about almost all the basic protocols and knowledge about Bitcoin, Bitcoin transactions, addresses, and how to protect your private key, you can just buy with any p2p platform. Centralized exchanges are better with this because I used one to purchase my Bitcoin but I don’t leave the Bitcoin in there, I do send it out immediately to my wallet for safety.
I don’t trust centralized exchanges with my Bitcoin, but I use them whenever I wanted fiat and when I wanted to trade, my asset’s safety is impotant, and I can’t held anyone responsible of any exchange get hacked or scammed.