Two very good websites that a Native speaker showed me to help with all these endings & nuances. :)
This first one I guess is aimed to help German middle-high school(primary?) students improve their native grammar and teach them English grammar as well.
This second one is a smorgasbord of German grammar things, it breaks down every little piece of the language, has verb carts, learn through music and reading, and a whole host of other things.
The second one I copied the url from the page that starts to get into the nitty gritty.
The second one is very helpful. Haven´t seen the first one yet. Thanks for sharing.