New to Plugins, please explain

Hello.

I am new to webdesign and using WordPress after trying my hand at Dreamweaver. (I actually liked Dreamweaver but a friend insisted I use WordPress)

Anyhow, I have these plugins in my plugins menu of course but they are just sitting there (activated). Am I confusing their function or how do I then utilize them?

For instance, I have a DocGallery plugin. So how would I then get this DocGallery to be functional on say, my gallery page?

I assume it is unlike widgets where you click and drag or install it to a specific page. Are plugins then managable by functions within WordPress’ side bar?

What am I missing?

Thank you!