How to calculate the session and engagement Rate in Adobe

In Adobe Analytics, Sessions are automatically tracked and referred to as "Visits" in reporting. Sessions is more of Google Analytics term so I assume you mean "Visits".

Simply drag the "Visits" metric into a Freeform Table in Workspace. This metric represents the number of times users start a session on your website, ending after 30 minutes of inactivity or when a user leaves and returns via a different campaign source. You can break down this metric by date, page, or segment to analyze session trends over time.

To calculate Engagement Rate, Adobe does not provide a default metric, but you can create one using a custom formula. First, define Engaged Sessions by creating a segment that includes visits where users spend at least 10 seconds, view at least 2 pages, or trigger an important event like video play or add to cart.(This is just an example and an Engaged visit can be defined you your business based on what's important to them). 
Then, use the formula: (Engaged Visits ÷ Total Visits) × 100 to calculate the percentage of visits where users showed meaningful interaction. Adding this custom metric to your Workspace report will give you a clear measure of user engagement.
You can also check the following articles for more details: 

https://experienceleague.adobe.com/en/docs/analytics/components/metrics/visits

https://www.linkedin.com/pulse/engagement-website-poornima-thakur-3s3rf/?trackingId=6E731H%2FqQBepbqVPnNhODg%3D%3D