When teeth first appear is as unexpected as the timing of baby's first steps, but in general, expect the first sharp nubbin around six months; some babies teethe earlier, some later. Heredity plays a part. If you check your own baby book, if grandmother was a tooth-record keeper, your baby's teething schedule may resemble yours.
Actually, babies are born with a full set of twenty primary teeth. They are just buried in the gums, waiting in line for their time to sprout. Teeth push through in upper and lower pairs, usually the lower appear before their upper gum mates, and girls teethe slightly earlier than boys. The "rule of fours" is how teeth usually appear. Beginning around six months expect four new teeth every four months until complete, usually by two-and-a-half years. Teeth come through gums at unusual angles. Some come out straight, other first appear crooked but straighten as they twist their way through. Don't fret about spaces. It's easier to clean between spaced teeth, and the spacing of baby teeth does not necessarily reflect how the permanent teeth will appear.