In sandbox, only the date/time and time warp controls are displayed. In science mode, your current science is shown there. When in career mode, you current funds, reputation, and science are displayed in the top center bar.
Whenever you first open a game in Kerbal Space Program, you will be taken to the Kerbal Space Center (KSC) scene.
The game's main menu presents you with the options to Start Game, adjust the in-game settings, visit the KSP Community website, visit Curseforge - a community driven mod site (replaces SpacePort), view the game's credits or quit and return to the desktop.
There are a few other articles that may aid understanding of this manual.