Not everything needs to go in a channel. Use Chat for private conversations with one person or a small group.
Everyone
Open Teams.
Click Chat in the left sidebar.
Click the New chat icon (pencil icon) at the top.
Type a person's name in the To: field. Click their name when it appears.
Type your message and press Enter to send.
To add more people (group chat), click the To: field and add more names.
Channel Post vs. Chat
Channel posts are visible to everyone in that channel -- use them for anything the team should see. Chats are private 1-on-1 or small group conversations -- use them for side conversations, personal questions, or things that don't need to be broadcast.
On desktop, you can hover over any message, click the three dots (⊕), and choose Pin to keep it visible at the top of the channel. Great for shift schedules, important announcements, or quick-reference info.