Nodes validate all transactions they receive. If a transaction is valid, the node sends it to other nodes.
Validation means checking if the transaction follows consensus rules. For example, one of consensus rules is that the total value of outputs must not be greater than the total value of inputs.
Nodes also check if the transaction follows their own rules. For example, almost all nodes reject any transaction with the fee rate of less than 1 sat/vbyte.
Note that a transaction with the fee rate of less than 1 sat/vbyte can be valid, but nodes usually reject such transaction.
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.
Transactions are not encrypted.
Miners include transactions in the blockchain exactly as they receive them.
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.
Transactions are not confirmed by nodes. Transactions are confirmed by miners.
Take note that confirmation means being included in the blockchain and that's different from being validated.
A miner (or a mining pool) that manage to find a block, sends the block to the network. Nodes receive the block and validate it.
Validation of a block means checking if the block and the transactions included in that are valid.