"Mi abuelo me enseña a hablar alemán."
Translation:My grandpa is teaching me to speak German.
Tye, there are a lot of verbs that use prepositions before a following infinitive. You just have to memorize them, because they don't always translate to English. Here's a very short list of verbs that need an "a" before a following infinitive: enseñar a (to teach), aprender a (to learn), comenzar a and empezar a (to begin), ir a (to go), venir a (to come), ayudar a (to help), and many more.