Confirm your motivation
Gardening is hard work, needs ongoing (often daily) commitment, and can sometimes require an investment of money to get started - and will always involve disappointing setbacks and even some failures. You need to be sure why you are doing it. Come to a studied conclusion about why you have this budding desire to grow green things, write down each motivating factor, and keep this list handy to inspire you onward to your glorious intent!
Take an inventory of all your available resources, and of what (or where) you lack, then go looking for what you need to get started. Space, water, sunlight and freedom from environmental pollutants are your big ticket items - soil can be bought or built, and seed, tools, etc etc are easily available and affordable to all of us. Knowledge deficiencies can be helped by good books and DVD's, by research on the internet (careful!), or very best by a local experienced gardener as mentor - you will always find them willing to help. But there is no substitute for your own learning experience gained by trial and error. So jump in, fail fast, and fail often! More to come...