your half pint jars are enough yeast to pitch directly if they're fresh. if they're not (i.e. older than a couple of weeks), consider a starter. IMO, for the average brew, dumping a half pint of older yeast into 2L of 1.040 wort to get it rolling again will get you where you want to be. if it's several months old, you probably need to go the extra mile and step it up.