You beat the Butterfly and you'll get an item or key from the tower, something that'll unlock a door at bridge where the Hellkite Dragon was frying people (next to where Solaire of Astora was standing). It'll take you down to a town street where you'll fight a couple of nasty hollow assassin and dogs. At the end of this area lies the Infamous Capra Demon. Once you kill him you'll get the key to the Depths, that's an ok area if it wasn't for the Basilisk. It inflicts curse, an ailment that halves your HP and can't be cured without a special expensive item, so beware. Unless it ambushes you, it'll go down easily. Clear the Depths and you'll face the Gaping Dragon, it'll drop the the 25k souls and I think the keys to Blighttown.
That is basically your itinerary for the next few hours. My personal advice is to buff your character in the forest, after you buy the crest, before heading into Blighttown if you feel you're under-leveled. The Spider Shied, which can be found in the Depths is a must (100% resistance to Poison and Toxic). A map of Blighttown wouldn't hurt as well. The first area can be confusing as hell.
Godspeed bro.