Start super basic, grow an herb or something like that in a cup of water. Go to a store and get one of the small potted herbs, take it out, clean the roots with water and stick it into a cup. This is super satisfying to see from a process stand point and a quick/easy win. After that start learning about different methods, and what each type of plant needs to thrive.

Hoocho's YouTube channel is great, already recommended below!