TensorFlow is better for Deep Learning and whereas Scikit-Learn is better for traditional Machine Learning. TensorFlow is better over Scikit-Learn because of its availability to do automatic differentiation. TensorFlow is better in faster computations because of the multiple processors but Scikit-Learn runs on a single CPU processor.
If you want to learn TensorFlow, I recommend enrolling in this Artificial Intelligence course by Intellipaat.
You can watch this video on TensorFlow in 10 minutes to know about the advantages of TensorFlow: