Students are often frustrated when trying to learn a foreign language because they can't organize the material like they are used to doing in other subjects. Language is fluid and we are able to finally understand foreign words when we let go and allow the right side of our brains to take over. Much of understanding is intuitive and contextual, so give yourself permission to guess what is being said or written. The key is to think through the words and let them come alive in your brain, so you can use them later. That's how you learned your native tongue. Grammar should be a supplement to your language acquisition, not the main player. I always recommend online courses with pictures, sound and familiar scenes between actors...like a play on stage, but in German.
You know the German word Kindergarten because you have heard it so many times in the context of your life. That is how you can learn new German words....find a program that has topics of interest to you in German. Juvenile literature is a good place to start. Go on ebay and order a 4th grade reader and you will be on your way. Share it with your children or grandchildren.