Here’s Leo, an online dictionary and much more, including discussions on word use and tables of declinations, conjugation, plurals, etc.
On YouTube, here’s Katja with her Deutsch für Euch channel with more than 50 episodes. She’s a grammarian, and a pretty good looking one at that. Episode 36 is a lot of fun.
Duolingo is a fine online language teaching tool. Give it a try!