Something that happens steadily occurs at a predictable, reliable, unchanging pace. If it keeps raining for hours, it's been raining steadily. If you stand outside without an umbrella, you will steadily get drenched.
Anything that keeps happening at a regular clip is happening steadily. A politician who campaigns every day for months has been campaigning steadily. If you write an hour a day on a novel, the novel is growing steadily. The opposite of steadily is unsteadily, which would describe something that happens in an irregular, shaky, or unpredictable way. Anything done steadily goes on and on.