The 3 most critical things for growing MJ is proper soil, proper light, and proper ventilation. Water and temperature and nutrients are all very important but fall under the other 3 in importance.
Proper soil: MJ doesn't like just any nutrients like most house plants(forget anything you know about growing house plants as it doesn't apply for MJ). There are 2 best ways to do soil(in my opinion). That is either organically(no fertilizers) or nonsoil medium(either soilless or hydro). I would highly recomend that you go to HD or Lowes or a garden store and ask for Organic soil. But if you go organic, you will absolutely need to go to the threads that cover organics and read read read. Also go to the book store and get the lastes copy of Skunk magazine as it has a super article on organic growing. If you are intimidated by organics, you can go with just regular chems in organic soil as several people here do that. They let the plants grow in the organic soil for a 5-6 weeks then begin adding in MJ nutes like General Hydroponics Flora 3part. Go to this website and just look through all of the stuff that they offer. There are many of these "grow-stores" online and shipping right to your door is easy and don't worry about law enforcement chasing the stuff to your door because they don't
Discount-Hydro.com
Proper light: MJ is a high energy plant, and like any high yielding fruit or vegetable plant, it needs as much light as you can give it without cooking it. The standard (if you don't already know) is (minimum)3000 lumens per square foot of growing space for vegging plants; (minimum) 5000 lumens per sqft of growing space for flowering. It is prefferable but not absolute that you use a lighting spectrum of 6500K for vegging and around 3000K for flowering. I don't know about that grow light from walmart. Many times those lights aren't in the correct spectrum to really help the plant grow, and they don't put out enough lumens. Many of us here use the T5HO florescent lights for vegging, however for a 2x2 grow space the T5HO will not fit well and give enough lumens. Your other option as suggested HB is to get an electronic ballasted MH/HPS in a small vented hood. Here is a website that I buy from as they are very reliable, but you can get good deals on Ebay as well(which is where I found this webstore the first time) hpsgrowlightstore.com
I would suggest a 400w system as well. You can start with the MH bulb for vegging and then switch to HPS when you get ready to flower.
Ventilation: with the new grow lights come heat. Too much Heat is a killer and must be removed. Having a fan on the plant is good, you will want to keep a fan blowing from under the plant as it grows. But that isn't close to enough for growing plants in an enclosed space(especially when its flowering time and total darkness is required during the 12hrs of dark time). Ventilation serves 2 purposes; Pulling out the heat, and plants breath just like we do and need fresh air that has lots of CO2. Just stirring the air with a fan doesn't work for that. You will need to buy a centrifugal type of fan that can be connected to the light by way of flex hose and routed so that the hot, CO2 depleted air can be removed, and fresh air can be pulled into the grow space. I recommend that you look at the different setups in the grow journals for examples of how people set up different vent systems.
As I am tired of typing, I will let another tell you about the other important parts of growing this wonderful plant. Welcome to your new addiction
smoking MJ isn't addictive but growing it definitely is