Hi @Pedro-Henrique and welcome to the Mattermost forums!
I think it depends on what it should look like and how users should interact with it. Mattermost is not a Wiki or anything where multiple people can contribute to the same article f.ex., so I’m not sure if it can or should be used as a knowledge base. You can create multiple channels and dedicate them to a specific topic, but you can not nest them so if you want to have a major topic broken up into a few minor and lastly smaller topics, this hierarchy cannot be created with channels. You can only have channel categories (but they’re actually per-user categories which you can have some influence on, but it’s tricky) and channels. Inside channels, you could use threads for the third level but I don’t think that this is practical.
There are some plugins which allow you to add notes to channels, like the channel notes plugin f.ex. and there are boards which allow you to create task lists and other content that may also be linked to a channel, but I’m not sure if Mattermost is suited for your usecase here.
Maybe I can think of something else if you can describe a bit more of what you would like to do?