How to use TM Dig in Pokemon Emerald

Hey so I just got TM Dig in Emerald but it keeps saying it doesn't work on the small indents, is it not supposed to dig there or is there something it to do before being able to dig?

Solution 1:

The "small indents" you mention are possible locations for Secret Bases. In order to interact with them, you need the Secret Power move, obtainable as TM 43 on route 111 and purchaseable from the Slateport City market stalls.

Solution 2:

The TM Dig, outside a battle, allows the player to come back at the entrance of caves or some buildings (including gyms), as it is said on Bulbapedia.

There is no other utility, like digging the ground to find items.