Hi Danyel,
"He told them to go to the restaurant" means he instructed them to do this action.
"He told them they would go to the restaurant" (notice I added the object "them") means he let them know that they would be doing this action. He may or may not have specifically instructed/directed them to, unlike the first sentence which means he definitely directed them to do so.
I hope my explanation was clear. If not, please let me know.