extensions

How to install extensions, for some reason i need to install some extensions

It works the same as with other browsers.
Download and install the add-on(s) that you want.

The question is if you really need them.
What is telling you that you need them ?
What add-ons are you talking about ?
A lot of sites are trying you to trick into downloading a malicious add-on.

I am glad you mentioned this. This is why 3rd party addons are disabled from Avast Safezone Browser. So you might find that you are unable to install these addons. What was you looking to install ?