Have you ever played the game where you all say one word at a time to make a silly sentence? Well, Google bombing is kind of like that, but with words on the internet.
Let's say there is a website about cats, and people want to make it really popular for fun. They might all decide to use the same word or phrase, like "adorable cats," and link it to the website. When someone types in "adorable cats" on Google, the website about cats will show up at the top of the search results because so many people used that phrase to link to it.
It's like a group of people all holding up signs that say "Go to this website about cats!" and pushing it to the top of the search results.
However, sometimes people use Google bombing for not-so-nice reasons, like to spread false information or make fun of someone. So just like in the game of making silly sentences, you have to be careful and kind with the words you choose to use.