PlugIns and the Loop – please help!

Hello everybody!
This might be an easy question for you guys but as a beginner I don’t know how to do this:

I’d like to add a couple of plugins and in the documentation it always says “add this little piece of code in the loop” – but where is the loop?

Lets say I’d like to add a counter under every post that shows the number of views. I can activate the plugin in the admin panel but I have no idea where I’d have to put the code.

So if someone could be so kind to tell me where the loop is and where I can edit the code to add plugins?

Thanks a lot
Yours,
Phillip