Check this link out, I'm sure it will help ya get started.
http/www.plantedtank.net/fertilizers.html
Generally you want at least 2.5 watts per gallon of light.
Take your tank size in gallons and divide by the amount of wattage your lights are.
(this is the most basic way to figure out your WPG)
Most of the ferts you buy in the liquid frm have dosing instructions on them so thats easy enough.
Other ferts can be in a dry form, theres a calculator I, or someone can give you a link too in the event you decide to get some dry ferts.
Then after you get the hang of all of it, you can start playing around with how often you fert and how much you add each time, there are general rules of thumb for this, but I find each scenerio is different with different needs that need to be dosed accordingly.
Test kits help you figure out exactly what you need with this type of dosing
schedule.
There is a link near the bottom of the page (the link above) that links you to " "Chucks Planted Pages".
Here you'll find a calculator to help you figure out how much of certain ferts you need to add to your tank.
It can and may seem overwhelming, but there are a tonne of people here that will help you through each step.