Once the meeting host sets up the meeting and invites you, you will get a calendar invite in your email. When it is time to meet, you can open the invite on your calendar and click Join Microsoft Teams Meeting link. It will look similar to the below image:
Please note that not all meetings will have a dial in number such as the example above. After you click on the link, if you have the Teams app on your computer or mobile device, it will open there. If you do not have it, you can choose to download it or join via a web browser:
Once you have joined the meeting, you will see several options. The first is to enable video if you have a webcam. The second is mute and unmute. The third button allows you to share your screen with everyone in the meeting. The fourth has more options such as recording. The last button ends the call for you. By default, you will typically be muted on entry. Click on the second button to unmute so you can speak. If your device has multiple audio input/output be sure to select the correct microphone and speaker in the audio options.