Settlements are reports sent by a channel that contains information about any order related fees, commissions, and taxes.
Some channels, like Amazon and eBay, have the settlements as a part of their feed. These get imported into SellerCloud automatically at regular intervals.
Other channels, like Walmart Marketplace, do not include the settlements in their feeds, and they need to be manually imported into SellerCloud.
More info on different channel's settlements can be found on these pages: