Your Jira admin sets up your default notifications. Depending on the project, you may get notifications when someone adds a comment on an issue or someone completes a work log entry. These actions tend to happen in short bursts, with a few small, individual changes added to an issue within minutes of each other.

Jira Service Management is one of their Software as a Service products. Anybody can create sign up for that product and then invite other people to access their copy of the product by entering an email address for the invitee. If you believe these are spam you can forward them to abuse@atlassian.com.

You can find the Base URL of your service instance by going to the Administration > System. Under General configuration > Settings > General settings it is listed. Atlassian Team members are employees working across the company in a wide variety of roles.