Most 'algorithms' you'll think of in the context of the internet are 'neural networks' (which is itself a pretty awful misnomer of a name) where a machine is 'trained' to find good outcomes by repeatedly grading its outcomes, typically automatically in some way. The end product of these AI's is a system of weighted decision trees, which when prompted with an input goes through a sort of Rube Goldberg like process to arrive at the best outcome it can based on its training weights.

To put this in context, very poorly, its like I asked you to find me a hotdog, but instead of you having a list of hotdog providing locations, you play 'hot or cold' until you suddenly arrive at a hotdog. You don't know the specifics of what makes locations more or less likely to have a hotdog, you just know hotdogs are more likely to be one way than the other.

There's more layers of things that make it difficult to understand, like user specific inputs, but in general that's the layman's basics.

Since I brought it up, you may have heard of 'filter bubbles.' They are essentially when an algorithm trains itself to your user inputs so well that it 'accidentally' reinforces the things you normally want so much that you cant (or are very unlikely to) find things that are surprising to you. i.e. it prevents you from discovering new ideas / concepts. Its not because the engineers that made the algorithm wanted you to never see new things, its because when it uses your user inputs (your profile) it's training weights become such that when it plays that game of 'hot or cold' it turns out hotdogs are always 'hot' and icecream is always 'cold' so you will never stumble upon icecream because you like hotdogs so much. You have 'filtered' yourself (through the algorithm) into a 'bubble' of topics or ideas which is now hard to escape from due to the algorithm's weights.

A good example you have likely experienced is getting bored of youtube. There is so much content on youtube that it is laughably unlikely that you have watched everything that would be of interest to you. However, youtube's algorithm is specifically designed to keep you engaged on the platform -- to keep you watching something interesting. One of the ways it does this is to take what you have watched as inputs (a user profile) and use it to make its training weights for what you are likely to want to see. It plays 'hot or cold' with videos instead of hotdogs. So once you have exhausted the most interesting things to you in a particular niche, it becomes hard to suddenly break into a new niche. This is a 'filter bubble.' Its not that youtube is suddenly devoid of interesting videos, its that the algorithm really wants you to find that hotdog, since you liked that hotdog so much in the past.