What are some of the best apps to start with? I like photography and music.
It depends on what you want to do. You may want to try iTunes and iPhoto, of course.
For playing YouTube videos as they were songs, try CloudPlay. For composing music, try GarageBand. if you want to edit music, try Logic Pro X.
For photography, you may want to try Aperture or Photoshop Elements or Pixelmator. Or the open-source GIMP.
There are several apps available in both categories (Music and Photography) at the Mac App Store. Just take a look.