I have no trouble with proving something by induction when I have a 'sum of' equation and an element equation, but I have no idea where to start with this:

Show that $\displaystyle m_n = 2^n - 1$ by induction for all $\displaystyle n \geq 1$

I have notes, but I can't make any sense out of them.

Can someone help me out in understanding the process for this question?

Cheers.