I am a little bit confused because you are a Senior Member on that forum but still you don't know how to buy a coin and trading. Whatever since you want to know about such things, you can buy or invest a coin from a centralized exchange or DEX, you can find most trustworthy exchanges list on the coinmarketcap, also here top coins lists.
I'm not surprised at all. The crypto space have moved on greatly from what it used to be. Before, all the alphas and knowledge were from only the forum. Now, even a newbie can learn so much from crypto Twitter or any other crypto centric discussion board and know much more than a senior men here. That's why in life, you have to keep learning regardless.