Hi, I'm also starting to learn German this summer! I did my GCSE back in year 9 but I've finished sixth form now and have done none since then, so I'm basically starting from scratch.
Personally, I wouldn't recommend starting with books, especially as this is your first language - you will look a word up, forget it, not follow the storyline because you were too focused on looking words up, become disheartened/bored and give up with the language all together. Save them for until you have the basics, and save TV/movies for when you are at a decent level. If you want to learn in a more authentic way, I recommend songs and possibly even children's poetry (not that I've ever tried the latter!). It's far easier to remember song lyrics than it is to remember individual words from a story. It also gives you an idea of pronunciation. I'm going through Rammstein songs and learning the lyrics - their songs have very clear, repetitive lyrics so it makes thing easy, plus I like their music.
In addition, I'm using duolingo and memrise, which are both free, very useful and perfectly suited to beginners. They are mostly vocab-based but include grammar notes which is great. If you're feeling brave and want to practice your speaking, italki is the best website I've found to connect with natives - you can pay for a language teacher or exchange knowledge with a German that wants to learn English.
Good luck!