The term "slug" is used to describe a collection of NFTs. For example, if we wanted to find a "Bored Ape Yacht Club" NFT, we would use the slug "boredapeyachtclub." The slug can always be found at the end of the search bar on https://opensea.io/ in the selected collection.
You can find the slug at the end of the collection link.
You can set a selected channel to post the announcements. In the case you do not see any channels you can select, or any new channels you recently made, you can refresh the channel list by clicking the arrow symbol (