The main 'Dashboard' section displays you information about your system, real-time CPU/RAM and Disk usage, as well as Network download and Upload speed.
'System Cleaner' section lets you delete downloaded packages resides in cache folder, clear Crash Reports, clean up System Logs, and Application caches as well. You should be very careful with clearing application caches, it will delete data created by the App or worse case scenario it may affect App performance or loading times.
You can choose the option(s) 'Apt Cache', 'Crash Reports', 'System Logs', 'App Cache' you want Stacer to do the scan and later you can clean it.
In the 'Startup Apps' section you can allow any application to start or disable application to not to start at boot.
'Services section is pretty interesting here, it allows you disable/enable services running or not in the background of your system session. By toggling a switch it makes much easier to disable core services as well such as Bluetooth, network, and so on. You must be pretty careful using this section, don't end-up with mess in your system.
Last one called 'Uninstaller' section, as its name tells you what it does. It allows you to remove packages, applications, core components of the system. Search box lets you refine the results you are looking for and filter down specific query. Again you have to be very very careful since there won't be any popups asking you 'Are you sure you want to delete this package?'. There is no undo button but install package again.