Soldier 76 is by far one of the easier heroes when I first started playing. His playstyle is pretty forgiving. He's got good movement speed / A self-heal / An ultimate that literally activates and aimbot for you.
As far as tanks go, I think D.Va is pretty good but I like Roadhog for beginners. He's super beefy, got a self-heal, and has a 1-shot combo that feels really rewarding if you can land it.