Welcome to MT!
You are a basic user
Then, you need to learn more here at MalwareTips!
First you have an AV, it is good
You should enable the UAC! (User Account Control), search it into start menu you will see
Keep your browsers and softwares up-to-date. And do
not use cracks and pirated softwares!
For your browsers, you need
Adguard Adblocker and
HTTPS Everywhere. These two extensions are essential and available for your both browsers.
You can use
HitmanPro and
Malwarebytes Free as a stand-alone malware scanner. These two will
not conflict with Avast!. If you use USB often, maybe you should consider to use
MC Shield USB Anti-MAlware Tool. All these softwares are free!
I hope these little words will help you to keep your PC clean for future and take a look at MalwareTips tips