LiquidCrystal::setCursor
void LiquidCrystal::setCursor(uint8_t row, uint8_t col);
This function puts the cursor at the specified position. The position is zero-based. If one of the arguments is outside the bounds of the screen, it will cause undefined behavior (bad stuff).
Usage:
LiquidCrystal lcd(8, 9, 4, 5, 6, 7);
lcd.begin(16, 2);
//I want to write two X at the middle of the bottom row
lcd.setCursor(7, 1);
lcd.print("XX");