F3 on Windows is what on a Mac?

On Windows to quickly search something, I just press F3 and then you can type what you are searching for as "keywords", how do you do this on Mac? I am busy with HTML and I want to quickly search something.

In general, to search for something on a Mac, Spotlight is what's used and can be brought up pressing: Command (⌘)-Space bar

Have a look at: OS X Yosemite: Spotlight keyboard shortcuts

If in an application, like TextEdit as an example, pressing ⌘F brings up Find.

Also have a look at: Mac keyboard shortcuts

You can use Command + F to search within Safari, Preview or most OS X applications..