When you get a calendar invite in Outlook, it will show you if there’s a conflict with other things already on your calendar. If you’re using Outlook on the browser, you now can pop open a display of your calendar to easily see what those conflicts actually are. Here’s how that works…
In this instance, Sandra sent me a calendar invite that happens to conflict with an existing meeting on my calendar. There’s a button that shows me there’s 1 conflict, and I can click on that to see my calendar for further information:

When I clicked the button, a calendar panel shows up on the right side of the browser window, showing all my meetings for that day so I can easily see what meeting(s) this invite is in conflict with:

If I want to get rid of that calendar display, I can click the Hide conflicts button. This is a great feature to allow you to get more context on your calendar conflicts without having to open a number of windows to figure things out.