Lalit owns 12 different books. He will take 5 of them on a holiday.

Step 1. Order? The same five books in any order make the same choice. So this is $^{12}C_{5}$.

Step 2. Work it out. $^{12}C_{5} = \dfrac{12 \times 11 \times 10 \times 9 \times 8}{5 \times 4 \times 3 \times 2 \times 1}$.

Step 3. Cancel. $\dfrac{12}{4 \times 3} = 1$ and $\dfrac{10}{5 \times 2} = 1$, which leaves $11 \times 9 \times 8 = 792$.