If you want to start in the world of digital animation, but don’t want to spend money, a great option is Krita. This program works for both illustration and animation. Some great features it has are onion skin and the importation of audio. Another great feature is that there are a lot of shortcuts for tools and many different settings for the pens. This program is really easy to understand and has a lot of similarities to other programs, so if you want to change programs at some point it will be easy to adapt.
So in conclusion, if you are searching for an easy-to-use program to start animating, Krita is for you.