When things or people gather, they get together in a group, or come together in one place. You and your friends might gather around the campfire, or gather on the soccer field to play together. Or, you and your family might gather at your grandparents' house for a special holiday.
And when you gather things, you look for them and bring them all together so you can use them. For example, if you're going to make a cake, you'll need to gather your tools and your ingredients, like a bowl, a spoon, a pan; and some flour, sugar, and eggs. It's a good idea to gather all your supplies before you begin a task.
If you gather some facts, or you gather some information, that means you learn it, or you figure it out. It's like you found the knowledge and put it all together in your head. You might gather a list of ten cool facts for a school project. And when I see that you're frowning and crossing your arms, I gather you must be upset.
If you gather your thoughts before an important job or a serious conversation, that means you take time to think carefully about all the important things. Like, what are my goals? What are the steps I need to take? How can I do this the best way? Gathering your thoughts is a good idea before you do something difficult or complicated.