After clicking on Files  from the left hand navigation in Teams, you will see the following Tabs

Home - From this tab you have the ability to view and edit documents. Recent will display those documents you have recently interacted with from Teams. 

My Files - Shows all files you have stored or shared in your Teams.

Shared - This view shows all files shared with you or by you in Teams.

Downloads - This view allows you to access all files you have downloaded from Teams.

To edit a document: 

Select the file that you would like to edit in the working screen. 

On the right hand side of the file name click the (...) More options button. 

From here you will have various options for editing the document: 

• Edit in Teams - This option is useful if you would like to edit your document in one place as it eliminates the need to open multiple different apps.
• Open in Browser -“ This option is useful if you would like to edit your file in the cloud, but do not like the look and feel of editing in the Microsoft Teams app.
• Open in Desktop App -This option is useful if you would like your file to automatically save and sync with Teams, and if you would like the full functionality of the respective program.
• Download - This is a useful option if you would like to download the document. 

Note: If you edit the document, the changes will not be reflected in the document in the Teams app.

• Get link - This is a useful option if you would like to share a link to the document with someone.
• Select which method you would like to use for editing.
• Your file will open with the respective program and method that you selected.