Can login be a use case?
User login or sign up certainly is a valid use case. There are requirements and expectations that the software must meet. The only things that are not valid use cases are things that either can't happen of the user does not care if they happen or not.
What is the main scenario in a use case?
A use case consists of a number of scenarios, each representing specific instances of the use case that correspond to specific inputs from the Actor or to specific conditions in the environment. Each scenario describes alternate ways that the system behaves, or it may describe failure or exception cases.
Should login be included in use case diagram?
If login is trivial and unimportant to the Use Case don't include it. Otherwise it would be good to include. Personally, I am in the habit of doing so. Primarily because in many of the systems I create, the logged in user may have any one of various levels of authentication or access permissions to other areas.
Is UHCL the same as uh?
University of Houston and University of Houston Clear Lake are fully separate and independent Universities within the same university system.