In answer to the titular question: Google it, obviously. But don't just Google it; start with the absolute most BASIC info sources you can find. Like if there's a "for kids" site that covers your topic of interest, start there. Then you can move on to more professional sources as you gain understanding, and (most importantly) you can stop before things start getting too complex for your purposes.
As for this steampunk robot character, I really think you should emphasize the aesthetic over all else. Like...it's not real. There's no reason for you to kill yourself trying to come up with a truly scientific way for something to exist when it just doesn't. Of course you're gonna have a hard time doing that; if it were easy, we'd have real-life androids walking around already.
Furthermore, 90% of people who go into something with steampunk themes aren't there to hear you describe the construction of all the wacky machines piece-by-piece. They're just there to see them. To hear about the gleam of the brass, the hissing of the steam, and the chugging of the pistons. Do that, do it well, and your readers will be satisfied.
If you do have to get into technical stuff, you could always just-- and I know this is insane-- make something up. Like, if your android character is having some mechanical issues, say they need a new combustion chamber, or intake valve, or ventilator unit.
I made those parts up just now. I don't know if they'd actually exist in a hypothetical steam-powered android, or if such parts even exist in real steam engines. But they sound like they do. To get heat for steam, you have to burn something- combustion. To direct and control the steam, you're probably gonna need some kind of valve. And every machine that generates heat will probably need a vent. Boom.
All the research you've already done will probably help you to come up with even more believable-sounding parts/issues. Although, yet again, 90% of your readers will not even care that much. Don't stress out too much about it.