Help using interfit light kit ex400 for photos?

Purchased and set-up soft box kit - there are 2 soft boxes, I connected my Nikon d3100 using a hot-shoe, however when I shoot the photo it is very dark. It seems I'm missing an important step.
The reason I purchased this was the ease of use I was promised at the photo shop. I'm Taking against seamless paper backdrop. I would like to have bright studio- like photos, for my fashion portrait shots.
Thanking you in advance for your valued help.

How exactly are you triggering the lights? These kits usually come with either a wired PC sync cord (which is not suitable for you as the D3100 doesn't have a PC sync port) or they've supplied you with some kind of radio trigger which sits on the hotshoe.

You can get a hotshoe to PC port adapter - is this what's on the hotshoe?

I will assume your lights ARE firing. My question to you is how are you setting your camera? You do realize you can't use any type of auto or semi auto mode on the camera don't you. You have to manually set an aperture and shutter speed to work with studio lights.

A starting point is to set your aperture to 5.6 and shutter speed to 1/60 and ISO to 100. Take a photo and look at the results. If too dark, then you have options available to remedy:
1. Open the aperture more
2. Increase the power of the lights
3. Increase the ISO
4. Move lights closer to subject

If the photo is too bright, you do just the opposite.

You have to set the camera and lights to work with each other for proper exposure. NONE of it will happen automatically if that is what you are trying to do.