I've been trying to understand the concept of bitcoin for a while now, especially its technical aspects, so I've been doing some personal research on my own, but I still find it difficult to comprehend some parts of it.
I learned during my research that a node is a computer on the blockchain network that sends and receives transactions with other nodes while also validating and storing those transactions and I also read that transactions on the blockchain are kept and encrypted within blocks and that a  block's transactions needs to be verified in order for a new block to formed.

I need more explanation because I still don't understand how a node confirms a transaction and determines whether a block is valid, it seems too complicated.