Hi! What do you mean by apps?
Do you mean phone/iphone apps? Because in that case, I wouldn’t be too sure what to answer… I do use the usual Instagram/VscoCam/Tumblr/Pinterest apps on my phone, just for little daily doses of inspiration when I’m on the go, but that’s about it. Would anyone else have any recommendation?
Or do you mean more like computer software? In this case you would probably need Illustrator, if you don’t already have it, and eventually more of the Adobe software like Photoshop or InDesign… I have no idea what your level in Graphic Design is, but if you’re only beginning, I would definitely recommend the simultaneous use of Adobe Illustrator CS6 Classroom in a Book, which you can find on Amazon. Also, you might want to invest in a drawing tablet. I have a Wacom one (also on Amazon), and I think it came with a few free downloadable software, which might be nice to start with.
Now that being said, I still think that nothing feels as good as a pen on paper! I use the Moleskine and Copic brands. I would also recommend to check out on some basics in books (Design as Art, Universal Principles of Design… ), magazines (Holiday, Kinfolk… ), and documentaries (Objectified, Helvetica… ). I would probably also take a look at the work of some of the big names of Design, or Art and Aesthetic in general, like Dieter Rams, Alvar Aalto, Mies van der Rohe, Irving Penn, Eames, Tomi Ungerer, or even Wes Anderson and Spike Jonze… (but this list is entirely subjective!)
Hope that helps! :)