Once you've finished onboarding, you'll receive a Teams invitation to your email with a subject like this: "You have been added as a guest to Yeshourun Digital in Microsoft Teams."
Open the email
You'll see your company name, beneath that, a purple button that says "Open Microsoft Teams"
Click "Open Microsoft Teams"
Create your password
Verify your email address
Solve a captcha or puzzle
Review & accept the permissions
If you're prompted to open an application, hit cancel
Click "Use the web app instead"
You'll see your channels (channels are like threads) on the left sidebar, beneath your company name. You should see a couple different ones: General, Maintenance, and maybe one or two more, depending on your use-case.
If you want to make a Service Request, read this.