Don't have a Microsoft Teams account? Sign-up for one here:
https://www.microsoft.com/en-us/microsoft-teams/group-chat-software?rtc=1
You will go through the following signup screens (enter your details):
You will be asked to verify your email address, phone number, and so on. If you have other accounts with Micro$oft, you might be asked if you want to transfer your phone number from one account to the other.
Setup involves several stages. Work through the steps in order, verify each stage before continuing, and keep a record of the configuration changes.