Self-Executing Files

I've been always curious about understanding about how virus carry out their activities. For that reason, I've read a lot of books and articles about different types of viruses and the way they operate in a system. One thing that I have never found anywhere and I am really curious about is this:

For instance, let's say I have successfully developed a virus and I've made it penetrate into a system. At this moment, what is the point, how that specific virus can start up its job. Do they automatically launch themselves without the user being involved ? I mean an event requires to be triggered to fire an action, if the virus is copied in the hard drive, what makes it run and carry out its evil duty ? I mean without being double clicked.

I found that in linux it can be done by writing certain scripts but when it comes to windows, I think the os doesn't have such feature. So I would appreciate you if you satisfy my curiosity.

There are many different types of viruses.

They are normally designed in such a way that they exploit weak security points in systems, applications and users' knowledge. Some of them are executed through user events, such as opening your Outlook e-mail reader and clicking on a link that loads a webpage that executes evil JavaScript (this JavaScript evil software is typically associated with scams or low profile commercial practices).

Some others exploit operating system user rights to write a hidden binary file to a directory where it will be executed from later on by exploiting another vulnerability at the application layer. Most viruses exploit more than one vulnerability to do their job and sometimes can be hidden in your system for a long time, awaiting a secondary event to take place and allow them to be executed.