SD-Library

In the description of the sd-library (sd.h) I find the functions under the title 'SD class' and 'File class', for example begin(), exists(),...., name()...rewindDirectory().
But in the example 'CardInfo' (in the Arduino IDE-examples) are used:

Sd2Card card;
SdVolume volume;
SdFile root;

and the(card.)init-function

if (!card.init(SPI_HALF_SPEED, chipSelect)) {...

I have no idea, how to use the init-function, what is 'SPI-HALF_SPEED' and so on and I didn't find any explications for that.
So, where can I inform myself to get a complete description of this library?

Thanks for helpful answers!

the CardInfo is not an example. don't use the low level classes and fuctions. CardInfo is there as test tool.

if you want to use SdFat, use the SdFat library