Well i've used lots of different programs!
I've used toon boom animate, I can't remember if it's free or not haha. I've also used photoshop a realllyyy long time ago, its not bad, but it's really not made for animation. I've used another one called Open Toonz, I believe the creators of Princess Mononoke used it to animate some parts of the film, its free too and isn't half bad. Now I currently use adobe animate, I actually like it and I'm able get it for free since I have a family member who works for adobe. I do think firealpaca has an animation set up as well, but i'm not 100% on that
No matter what program you use, its gonna take a while to get used to since most animation programs are completely different from normal drawing programs!