If the boulders are smooth then you need to get one of your Pokemon to learn strength to move it and if the boulder is rough then you need to get your Pokemon to learn rock smash ( both of these moves require HMs to be learnt)
Chat with our AI personalities
You have to meet other people and take their flags in the Underground.
you can use the hm strength you can smash rocks with rock smash
You use Strength to roll the movable boulders.
you have to obtain the HM strengh and teach it to a Pokemon in your party. after that just stand in front of the rock and press the B button.
Get strength by finding the wardens teeth in the safari zone and he will give it to you.