When you're chatting with one or more people in Teams, you can instantly share your desktop or screen. Go to the chat controls in the upper-right corner and select Start sharing your screen .
Choose a window to share that specific program and its content, or select Desktop to share everything on your screen.
The other participants in the chat will receive a notification asking them to accept your screen share. Once they do, they'll be able to see your screen and continue the chat.
When you're done, select Stop presenting at the top of your screen.
Note: Add voice to your screen sharing by selecting Let's talk. The people in your chat will receive an invite to turn on sound and once they accept, you'll be able to talk.