First to use Microsoft Teams on your Apple device you will need to download the free mobile app from your app store.
Apple iOS Devices
On your Apple device look for the App Store and open as shown below.
Please note – The below screenshots are taken from an iPhone X. Please make sure your device meets the requirements to use Microsoft Teams on your Apple devices. You can find the hardware requirements here. Please note Microsoft recommend to use the latest updates.

To search for the Microsoft Teams App in the App Store click search icon with the magnifier glass on the bottom right

Type Microsoft Teams in the search box and click search button on the keyboard

Select Microsoft Teams
Click GET
Click Install

Sign in with your Apple ID if required by entering your password to start the download to your device.
Once Microsoft Teams is downloaded you can click OPEN

This will open the Microsoft Teams App on device
Here you are prompted to select one of the following to start using Microsoft Teams
Sign in with an account
Join a meeting
Sign up for free
