The Block Gas Limit is the maximum quantity of gas that may be consumed in a single block and is used to decide how many transactions can be crammed into a single block. For example, if the block Gas Limit is 100 and there are 5 transactions with Gas Limits of 10, 20, 30, 40, and 50, the first four transactions will be successfully packed into the block. The miner has the authority to choose which transactions are included in the block. As a result, another miner could opt to load the latter two transactions (50+40) into this block before packing the first transaction (10).
If you submit a transaction that hasn't been finished and has spent more Gas than the Gas Limit you specified, the transaction will be cancelled, and the fee will be taken as well - to compensate the miner who has already put in the effort. The transaction service fee is charged for the actual Gas consumed if the transaction is completed and the Gas consumed does not exceed the Gas Limit.