How to embed webdriver browser into java GUI/ attach to exsisting browser

Im new into programing and foun that selenium webrdiver is very powerful tool however I cant find way how to embed browser into my GUI and still be able to drive it.
Also every time starting code selenium creates its new browser window. But its possible that launcging my code first time it would create new browser window and for the second time I launch code it would attach to that already opened window instead of creating new ones?

English is not my native language so sorry for my mistakes.

Every time you run your code, your code might be having something like

Code:

new FirefoxDriver()

This creates a new instance every time and opens a new browser window.

In order to use the same session, you may need to write your code such that the webdriver is singleton i.e one webdriver instance per JVM.