After you log into oGame, you can choose to view the galaxy around you.
You start out looking at your local system, but you can either use the arrow buttons to switch the system (or the galaxy) or punch in specific coordinates you want to view.
Keep in mind that every time you view a galaxy or system, you use 10 Deutrium. This can really eat into your Deutrium supply at the early levels of the game, so be aware.
As you progress onward and upward, spending a couple hundred deutrium to view multiple galaxies and systems isn’t that big of a deal.