The ISP (Internet Service Provider) is your mailman. They need to get packages to where they need to go. HereBeAnswers, for example, is sending you a package containing this answer. You pay the mailman monthly for a rate at which they send packages from you and to you.
HTTPS encrypts the package’s contents, however the ISP’s responsibility is still to move the package from A to B, and therefore needs to know what these A and B are. Therefore the postage address cannot be encrypted, and your ISP can track who you are exchanging packages with, be it HBA or YouTube or Netflix.
So your ISP can’t actually see what you are viewing on HBA, YouTube, or Netflix, but they can see which sites you are accessing.