Your computer GPU or graphics cards are utilized to hash out (calculate) an algorithm which clears transactions on the blockchain. Each time someone sends for example a bitcoin transaction, they pay a small miner fee to validate that transaction...That miner fee is given to the person who solves / finds the block with that transaction in it as a reward for their time, energy use, etc
Another way to explain it is to think of yourself as a teller at a Bank getting payed for serving customers...Except the Bank is Bitcoin and the customer transactions are on the blockchain.
Some other important things to note
a) there will be difficulty adjustments on the blockchain meaning you will earn less and less of a reward over time for the same amount of hash power. Often people will switch between different coins.
b) there are different algorithms..this means some GPUs perform better for certain algorithms.
c) ASIC Miners are basically a GPU bundle specifically designed and optimized to mine a specific coin or type of algorithm...where standard GPUs can be switched between different algorithms
d) PoS - Proof of Staking is similar to PoW, but more eco-friendly...You leave a cryptocurrency wallet open and connected to the internet, with some altcoin inside which does the same thing as a computer (solves hash to earn a reward for finding a block), but obviously with allot less electricity because you can run it on a small computer like a Raspberry Pi, laptop or Intel NUC
Terms: Hash Power - GPU power in solving an algorithm.
Algorithm - advanced mathematical equation
Hash - An unordered association of key/value pairs, stored such that you can easily use a string key to look up its associated data value. (you'll understand this terminology better if you learn Python or a similar programming language)
Disclaimer: I am a bit tired when writing this article
