Little question

From what i understand,Avast is scanning every file i open(i assume it since the icon is spinning every time i open something),other anti viruses are doing it too? or its something that is unique to Avast?
Thanks in advance.

Avast is a resident (on-access) antivirus.

Not all files are scanned when opened only those which are susceptible/targeted by malware, these are files like .exe files but many other file types are included, those that have been/can be infected . Whilst this isn’t unique to avast, it is at least showing when it is scanning by rotation of the avast tray icon.

The fact that avast scans multiple areas, files on your system, web sites that you visit and emails that you receive or send. So it is quite extensive. Depending on what modules you have installed and what avast version that you have, it can be scanning quite a lot.

From what i understand,Avast is scanning every file i open(i assume it since the icon is spinning every time i open something),[b]other anti viruses are doing it too?[/b]
Yes, all antivirus with real time protection (i only know one that dont)

Wikipedia >> https://en.wikipedia.org/wiki/Antivirus_software#Real-time_protection

Real-time protection
Real-time protection, on-access scanning, background guard, resident shield, autoprotect, and other synonyms refer to the automatic protection provided by most antivirus, anti-spyware, and other anti-malware programs. This monitors computer systems for suspicious activity such as computer viruses, spyware, adware, and other malicious objects in ‘real-time’, in other words while data loaded into the computer’s active memory: when inserting a CD, opening an email, or browsing the web, or when a file already on the computer is opened or executed.