Game development is one of most difficult disciplines in software development, mainly because it involves so many different fields. Not only do you need to program the gameplay, you also need to produce high quality art assets and audio.
You may have the good fortune of being on a team with dedicated artists and audio engineers, but it's also possible that you are tackling this difficult task alone, with the goal of learning to produce art and sound effects along the way.
If you find yourself in such a situation, here’s a great tutorial for Aseprite, a very popular pixel art software. Although pixel art is not necessarily easier to produce than other types of graphics, it’s a popular choice for beginners. Aseprite is a great tool that provides you with a full suite of tools to help you make pixel art for your games.