The normal way is written on the back of the bag but i have found it is much better to do it the way i am about to tell you because the plants know right off the bat whats expected of them.  We roll the handle to make it stronger and we hang it up and fill it with moist soiless mixture ( I recommend Pro Mix Bx ).  You start on the bottom and either skip the bottom two ( they generally get too wet and die anyway so just skip the bottom two) get a nice stick or poker of some kind and poke the first two holes straight down not straight into the soil.  DOWN is very important because you want to get the roots to hold the plant up.  Insert the first two plants in these holes.  Next the two holes above the ones you just planted,  you do exactly the same thing,  poke those holes STRAIGHT DOWN and it will close the ones you just finished.  After you poke that set of holes, you put little plants into them with the roots going down, not in.   You do exactly the same thing again,  Poke the next two holes above the ones you just planted and it closes them and makes the place for the next two plants at the same time.  Continue as above until you have all the slots planted.    I have found that if you skip the very top it makes it easier to fill with water for watering in the future.  If you want though you can put one plant in the very top.   

The very best plants for these bags are purple wave petunias or a  begonia.  Waves are really nice but they are so  hard to keep watered during the growing season.   If you want to use them just skip each layer of holes and use less plants or just do either side back and forth.  They get so big anyway you wont even know you didn' t plant them.   The begonias are really nicer 'cause they will be alot less tempermental about the watering.   What-ever you do, dont think you can do strawberries or tomatoes in these bags.   There just isnt enough soil to make them do well. The very best are the begonias as they have lots of colors to choose from and they will cover the whole bag really nicely and you can keep them watered the whole season.  Miss a watering with a begonia and they will keep blooming like you did it perfect.   Miss a watering with a wave or something else and you will pay in the long run.  I say you should water them every day with at least a quart of water.  Fertilize every other time or every third time.    They make a great planter and will hang on a fence or beside the door wonderfully.  They have a set of tiny holes in the bottom that drip away from the surface you hang it on so its really a nice convient way to grow things in a space thats usually not plantable.