There are four places you can go in Teams to add an app.
Not sure why you’d want to add an app in the first place? Get an overview by reading Five things to know about apps in Teams .
1. Add apps from the left side of Teams
Go to Apps on the left of Teams, then search for your favorite app or browse the app categories to find new ones.
Select the app you want and a description screen will open. Take a moment to browse the subsections (e.g., Tabs, Messages, Personal app.) This area explains the capabilities of the app—and where it will show up in Teams, ready for you to use or configure.
As far as adding the app goes, just hit the Add button! This step is the same from every location where you can add an app.
Note: Team owners can restrict who can add apps. Some apps can be installed only by a team owner, as they require additional permissions.
2. Add apps to a tab in a channel or a chat
In tabs, you can add apps to share content and work collaboratively
Go to the channel, group chat, or one-on-one conversation of your choosing, and click Add a tab 
.
From there, select the app you want. In some cases, you might go on to add a specific file to the tab.
3. Add app notifications to a channel
An app capability called a Connector inserts app notifications into a channel.
To set one up, go to the channel you want, select More options 
> Connectors, and choose an app.
You'll be given the option to Configure notifications for any app already added for your team or to Add a new app.
4. Add apps from the messaging area
Some apps let you insert content from the app directly into Teams messages. To add one, select beneath the box where you type a message and choose an app.
Another way to add apps is to type @ in the box then click Get bots.
Bots provide answers, updates, and assistance when you chat with them one-on-one or in channels.
Watch how it's done!
At this time, adding apps can only be done from the web and desktop versions of Teams.
However, once you set up notifications or bots, they work just the same on your mobile device as on desktop. And, many of the apps you've added to tabs will appear at the top of a channel under More.
App availability in mobile tabs varies by company that created the app.
