To begin researching some executable or library in Ghidra you actually have to create project and import file to it.
- Launch Ghidra, then press File --> New Project
It's time to add some files to your project.
- Open the project file (.gpr). If you've already launched Ghidra click File --> Open Project when in main window.
- After you loaded the project, pick the file you want and DRAG&DROP it into the Ghidra start window. Also you can import file using the menu File --> Import File.
- Ghidra detects the file format. When reverse engineering different crackmes on Windows OS, the default choice (PE - portable executable) is fine.