To use Bing Webmaster Tools, you first need to create an account. You can sign up with an existing Microsoft, Google, or Facebook account.
The next step is to add and verify your websites. The verification step is needed to prove that you are the owner of the web property. Read the verification methods available.
Another way to verify your websites is to connect Bing Webmaster Tools with your Google Search Console. This will share effectively data between the two services.