start reading the hundreds and thousands of guides, posts, and general advice from everyone on this site. imho, your first post should be done until you have thoroughly read and at least, think you understand, all of the stickies in all topics. ill go through what i did before i even registered on the site:
start with newbie central and indoor growing. get a solid understanding of lighting (as to what a plants needs are and when), exhaust, necessary temps and humidity, as a plant will only be as good as the environment you give it. once you have this figured out, you can build a suitable cabinet/room/box/whatever to actually grow in, and not find yourself with a crisis later on. (you dont actually need the area built to move on, but its nice to have an idea of what you want to do before you become active on the thread, that way you can provide better details for more specific help)
then move on to the basics of growing, things like watering, nutrients, and signs of deficiencies. these can be found in Marijuana Plant Problems. you will find there are a lot of things you will want to monitor over time, but starting with the basics really helps. water ph, soil mix, and (in my case) relative humidity can have a big impact early on in your grow, and you will want to be prepared.
start with these threads, and i mean really read them. get the info from them down. if your seedling just got in the dirt, you have at least a month until sexing. this gives you lots of time to read read read and READ some more! i was browsing threads here damn near 40 hours a week for a while, but i learned a lot fast, and its worth it. by the time your switching your light cycle, youll have a really good idea about the whole process, and be preparing for your first whack at, well wacking plants (harvest lol). it is during that harvest, that all the ideas about what you did wrong, what you did right, and what you want to experiment with next time, that will be rushing through your head. i digress, here are those threads, enjoy!
Widow Makers 101 Already Asked Questions,
Widow Makers How To Grow,
Ceestyle's Lumens Thread. These will provide you with lots of answers, and hopefully, lots more questions as well. Either way, it should be a good amount of reading for you. Good Luck