Does each block contain all the Bitcoin transactions for that time period? When a miner validates a block, does the block contain all transactions in Bitcoin for that time period? So does a miner validate an individual transaction between two parties, or are they validating transactions between all the parties in Bitcoin for that time period.

When you read examples about a transaction in Bitcoin, it makes it seem like each individual transaction (e.g. 1 Bitcoin from Bob to Alice) is its own block, validated by a miner.
The process of a transaction being created and included in the blockchain is as follows:


The sender creates, signs, and broadcasts the transaction
All Bitcoin full nodes, including miners and regular users, receive the transaction and validate it by making sure it follows the Bitcoin protocol rules
Nodes temporarily store the unconfirmed/yet-to-be-mined transaction in a database called the "mempool" (each node has its own copy of the mempool)
Miners combine many transactions from their mempool into a single block. They will put as many transactions as they can fit into a single block (based on the Bitcoin protocol rules)
Miners begin hashing the block until they come up with an acceptable hash (this is proof-of-work mining)
Once they have successfully "mined" the block by getting an acceptable hash, they broadcast the block to the network
All full nodes receive the block and check to make sure the block and the transactions within it are all valid with regard to the Bitcoin protocol
If the block is valid, nodes add it to their copy of the blockchain. They also remove the transactions within the block from their version of the mempool
Non-mining nodes sit and wait for more transactions/blocks to come in for them to validate. Mining nodes go back to step 4, bundle more transactions into a new block, and repeat the mining process