Finding Simple Custom Reports & Charts
Jira Cloud
Simple Custom Reports & Charts app adds menu items in two places on your Jira instance (if no menus are visible after installation, you might need to refresh the page).
Space sidebar menu (highlighted in blue) - the app starts with reports on work items in the current space.
User account menu (highlighted in green) - the app starts with reports on work items assigned to the current user.

Jira Server
Simple Custom Reports & Charts app adds a link to the main menu of Jira, the app starts with reports on work items in the current space.

Dashboard Gadgets
In addition to preconfigured reports (Space, User, Epics), the app also allows you to add custom5 dashboard gadgets as native Jira dashboard gadgets.