SIM808 GPS/GPRS/GSM TEL0097. Question about instructions in code (Read SMS messages)

I have question about code for the shield (Read SMS messages).

https://www.dfrobot.com/wiki/index.php/ ... U:_TEL0097

What means this instructions? Sorry, if it's silly question, but i have no idea

char phone[16];
char datetime[24];

Thank You in Advance for answer