Note: These instructions are for accessing the basic Enterprise version of M365 chat. If you are interested in M365 Copilot (add-on license) which has more features and costs an additional $30 per month per user, see this article.
The chart below details the differences between the two plans and is taken directly from this Microsoft page.

Accessing the Basic M365 Copilot Chat
Step 1: Open an internet browser (e.g., Google Chrome or Microsoft Edge)
Step 2: Go to https://copilot.microsoft.com
Step 3: Click the Sign in button in the upper right corner.
Step 4: Select the Continue with Microsoft option.

Log into BSU.

Step 5: Select the Work experience.
