First,you have to be in Nimbassa City, go to the Battle Subway (tallest building there), enter the Battle Subway, go forward untill you see a maroon sign and if you read it it says "Train to Anville Town". Talk to the man in the man in the green shirt, and your in Anville Town!
And it is NOT a useless town, once you get there, there is a set of houses and the 2nd one to the right, has a green shirted man, he'll give you items like Carbos and stuff like that. The first time you talk to him he gives you Rare Candies!!! Rare Candies are VERY useful and that makes the town VERY useful, but he'll only give you items once every 3 days.