How can I get back to an open app or Google search after I use other apps?

Sometimes while searching Google from my Google search bar on my S10+, I may open another app to do something else. Then, when I return to my home screen and access Google, my search results are gone and I must start fresh. Likewise, I may have an app open and then open a different app. Later, when I want to return to the first app, it apparently closed and I have to start over again. How does one go from app to app without losing your place in an app opened earlier? Like in Windows, where I can click from tab to tab and go back to anything that I opened. Thanks.

If your using navigation buttons it's the recent button (three vertical lines).

Thanks! Actually, I haven't tried them as I really didn't know what that icon was for. I though it just made multiple, small windows open across my home screen. I'll try that.