Simple, just pour your slap pack, yeast vial, or starter into the fermentation vessel and airlock. Be sure that your wort temp is below 75'F for ales. Normal fermentation temps are 65-70'F then for ales, though each yeast has its own optimal fermentation temps, so check it. Keep in mind that during krausen, you will probably need a blow off tube, or you risk a huge mess. Also, keep in mind that during active fermentation, the vessel will typically run 2-4'F hotter than the ambiant air temp.

Now you just wait. I typically allow 1 day for each degree Plato of original gravity in primary. That means typically, 2 to 3 weeks, minimum. I have gone up to a full month, though it is best to probably transfer to a secondary off the cold break (precipitants from the wort and yeast interaction).