My son's iBook G4 booted in Terminal mode.

Black screen with white letters indicates the full operating system is not properly installed. Command-S will force the machine to boot in this manner as well,

and if it is depressed, then there is no problem with the operating system, the file system check will usually indicate if it can be booted normally.

White screen with black characters indicates the open firmware is being booted into. Typically happens if the PRAM battery or capacitor needs replacing, or command-option-o-f is pressed at startup either deliberately or through some short of the keyboard.

An iBook G4 800 Mhz can max its operating system at 10.4.11.

An iBook G4 867 Mhz (1 Ghz) or higher can max its operating system at 10.5.8, but can't run Classic once put at 10.5 or above.

Identifying your iBook G4:

https://discussions.apple.com/docs/DOC-6413

is key to knowing what operating system it can run.

Usually the info on the battery bay indicates what model and age of model it is.

For what it's worth, there is no PRAM battery in an iBook. Settings are held by a capacitor.