I thought you actually had to get a mission before you could go to a town. Apparently not? Anyway, since the mission are moving continually to the west for the most part, its to the west of the starting point. As said in another thread on this same subject (that you started), the tank is probably in Coldwater or something like that (starts with "Cold"). It's the 13th mission. You *will* need energy weapons to do much in the mission, since there will probably be robots and people in Power Armor to contend with. The location of Coldwater is to the southwest of the starting area.
Now, as Miroslav so tactfully stated, why don't you go play the game properly and find out where the damn tank is instead of repeatedly asking the same question? Since you can only use vehicles in random encounters and on certain missions, having the tank won't help you a whole heluva lot unless you're supposed to have it.