New to ML and NLP. Is topic/subject extraction a good place to start?
You could learn about word embeddings. These will provide you a natural path to topic models, and many other NLP tasks. Look up word2vec.

I think it is better not to learn two new subjects (NLP and ML) at once. I would start with ML on its own; take this class perhaps. A good place to start is linear regression, or binary classification.