What software should I use to design the graphics for my android app?

The industry standard for graphics production is the adobe creative suite of products, Though there are others out there, Adobe Illustrator is used for vector graphics which are resolution independent ie they will scale to any size and the will will look the same albeit bigger or smaller, this is ideal for logo's and some illustration work depending on the style of illustration you want(vector programs are not good for painterly style illustrations) and buttons as well , Photo shop is also used for graphic work, It deals with image and photo-manipulation and is resolution dependent, ie depending on the settings the work will get pixelated once the image is enlarged to much, also photoshop is also used widely for creating digital paintings as well, Again adobe suite is the gold standard and is the among the most used graphic programs in the professional market place, however there are other alternative more inexpensive programs out there, albeit maybe with a bit less functionality, The adobe software suite does have some 3d functionality to them, however if you need some serious 3d rendering 3dmax, maya, and a few others are the go to for those such things . to answer another part of your question, your assets will need to be created by someone, there are a lot of clip art and image libraries, Icon libraries, and stock vector art-work some of it you can find for free. searching for the right assets is time consuming, and has a possibility of making a cookie cutter end product. like I said there are other programs out there that may be a better entry-point for you than the adobe software suite. since the learning curve on these programs is steep just for the fact that they are so huge. I would do a little research and see what alternatives people are enjoying using. If you are planning to go to business yourself and market your own apps rather than work at a development firm, I would suggest finding yourself a graphic-designer that you enjoy working with. If you are on budget, I would find a design student at a design college or the public universities. However be prepared to pay a fair wage. For a design student in training I would feel that would be about 15 - 20 an hour. Most will charge on a per project basis, you can have them draw up a contract based on what they think the work would be worth. Also think of the graphic designer not as a hire but a collaborator, as you are educated on engineering, and development side of the project they are just as trained in the art of visual-communication and will offer great insight into the visual aesthetics of your project.