Reach out to the community
Animation is art, and the community must feel for, love or hate, your art!
Our communities are the most valuable resources for cooperating about our endeavours and to get help when we run into stumbling blocks. When it comes to communities in the creative arts, they’re a great place to show the fruits of your labour. The largest one is deviantART, where you can search for the software you’re interested in and see what others have created with it. This will help you assess if you can achieve your animation goals. When starting out though, you need to get help for the tools. Let’s see where to go for help for the tools themselves…
Synfig has a great wiki that also comes in handy for asking questions about functions and techniques. There are also many tutorials on YouTube, if you need more advice.
Blender has both technical communities and special artist communities, there is even a number of people that make a living animating with, and teaching, Blender techniques.
Pencil2D has a wiki on its website which is moderately active. The program has many dedicated followers on deviantART. Many users choose to use Pencil2D for its simplicity because you draw as you would on paper.
Tupi is originally from Columbia so a lot of the content is in Spanish. Having said that, the program has a few but well-defined features and the tutorials that are in English are well written.
GIMP has several sites dedicated to it and some discuss animating using the filters and the GAP extension. These are useful for getting more help. Remember that GIMP has been around for a long time so anyone interested in graphics and open source will know this software well.