Were steam trains used a lot?

Yes. Used a ton. The steam locomotive was, for a long time, the only way to power a train.

When diesel-electric locomotives proved better for railroads in the 1950s, they became less used...

But from 1830s to 1940s, they dominated, basically. I mean, yeah, there were electric only railroads, and diesel-electric locomotives around, but steam was basically the main power for America.

Other countries, steam was almost only what they used. Japan and China would be some countries that slowly developed rail systems. Both countries continued revenue service with steam locomotives up into the 1980s.