Well, you (correctly!) wrote the definition yourself: 7 to the 7th power is 7 multipied by itself 7 times, which is exactly what you wrote.
If you want to evaluate this expression, just put this into a calculator (watch out: powers grow quite fast, so this is going to be a big number!) to get
[tex] 7^7 = 7 \times 7 \times 7 \times 7 \times 7 \times 7 \times 7 = 823543[/tex]
