What beer are you making? If you're making a 5 gallon beer under 1.060, then a starter isn't that necessary. If youre venturing to higher gravity beers, then you should be looking at starters now. There are several "techniques" for a starter...but the basic principle is that you make a 1.040 DME batch that you pitch the yeast into. The size of that batch is determined by how big your beer is. You then either use a stir plate, or swirl the starter every once in awhile, to keep it aerated. The starter is done fermenting when you see a big sediment layer on the bottom and relatively clear "beer" taking up much of the volume.
As for "is it too late"...no, as soon as you take out your yeast from the fridge and raise it to room temp....it's now a viable, pitchable yeast. The main thing that you're doing when you put a batch of yeast in the fridge is that you're making those yeasties go to sleep. If you've gotten a slap pack to swell up, that just means you've gotten some yeast to multiply. Those new yeasts still will either go to sleep or set forth and binge depending on what temperature and food they have.
On Tap: Barleywine, Coffee Oatmeal Imperial Stout (big big beer)
Fermenting: Double Simcoe IPA
On the Bench: Racer 5 IPA
"One of the first things early caveman did, when he crawled out of the mudd, was to make beer. And cavemen everywhere are still making beer...and drinking beer." - Jean Sheperd