What are you confused about? Sketch is basically vector software intended for producing user interfaces such as websites and apps. You can use other software like Illustrator or Affinity to do the same job, but Sketch is built from the ground up to make it faster and easier.
illustrator for me going back 15 years. I started on Corel Draw, but switched once in an agency and never looked back. I haven't tried sketch though. I would say it comes down to what is most comfortable and efficient for you to get your ideas down into digital vector format and then manipulate to perfection.