When you're in a chat, you can send messages that include files, pictures, and links.
Send a link
To send a link, select Format beneath the compose box, then select Insert link .
Add display text and the address, and then click Insert, or simply copy and paste the link into the compose box and select Send . Once you send it, the message containing your link includes a thumbnail image and preview, which you can close if you'd rather not see it.
Include a file or picture
To include a file or picture in a message, click Choose file beneath the compose box. Then you can upload an file or picture from your computer or OneDrive, or search for one from the Files tab for that channel.
In a chat conversation, click Choose file and pick the file or picture you want from your computer or OneDrive.
Send a link
Just enter or paste a link into your message compose box.
Attach a picture
To attach a picture to a message, tap Add photo beneath your compose box to take a photo or to open your photo library.
Attach a file
To attach a file to a message, tap Choose file beneath the compose box and go to the file location.
From a chat or meeting, tap the attachment to open it with an Office 365 app. In a channel conversation, tap the attachment or go to Tabs > Files.