But this example is more complex for me.
Do not exist any library for read-write data more simple?
to complex? The sketch is a one-file-solution: the lib-functions to talk to the board are included, that's why it looks so complex.
You can replace the loop function with the following (untested) code:
int block=0; //TODO: your block number
if (selectCard(true) &&
MFRC522_Auth(PICC_AUTHENT1A, block, defaultKeyA, serNum) == MI_OK &&
MFRC522_Read(block, buffer) == MI_OK)
//TODO: block buffer contains the read data
if you want to read 1 block only