Imagine that you are a Bitcoin miner, and each time you want to enter your block into the blockchain and get a reward, you would be given a combo lock and would need to guess that combo in order to enter your block. Now let's say that your computing power (hashrate) is the number of combinations you can guess in a second. So the more computing power you have, the faster you would guess the combination. Since the Bitcoin network wants to keep the time between blocks created in the blockchain constant, as more miners or computing power is added to the network, the harder it becomes to guess the combo. Just imagine that as more and more people try to guess the combo, you will be given locks with more possible combinations. Essentially, a hash is just a method used to guess the combination for the lock.