Hi, if you mean with code then you should check the file active.php which is in ./actions/admin/plugins/active.php 

You will see that the code gets the entity and then just execute $plugin->activate();

I hope this helps.

Why would you want to do that?

You could change the manifest.xml and set to activate on install.
 

Thanks a lot guys

and to the question "why would i want to do that"
i am trying to upload this website but it isn't working

I don't know what exactly is not working for you but I'm pretty sure that your problem won't be solved by trying to activate plugins in any uncommon way.

Try to install Elgg the normal way, check for entries in the server logs if it fails to get installed and if in doubt ask here on the site for possible solutions to the problem.

I agree with iionly. What error are you having? What is the problem?

So? You solved your problem?