Link to article: https://support.microsoft.com/en-us/office/share-files-in-teams-0c4d34ee-5dd8-46d5-ab35-0d227b5e6eb5#ID0EBD=Desktop
If you can access a file on your device, you can share the file with other people in Teams. This includes files (of any type) that are:
And there are two ways to share files in chat messages:
-
Send the file itself.
-
Send a link to the file.
Share a file in a one-on-one or group chat
-
Select Attach 
beneath the box where you type a message, and then either OneDrive or Upload from my computer (depending on where the file is located).
-
Select the file and then select Share or Open.
This will upload a copy of your original file.
You can also upload a file by going to the Files tab and selecting Share.
Share a file with your team in a channel
-
Select Attach beneath the box where you type your message in a channel.
-
Do one of the following:
• Select Recent to choose a file you recently opened, and then select Upload a copy.
• Select Browse Teams and Channels to choose from all the files you have access to in Teams, and then select Upload a copy or Share a link.
• Select OneDrive or Upload from my computer (depending on where the file is located), and then select Upload a copy or Open.
You can also go to the Files tab and select Upload.