Toilet training is a fairly complex activity.
The idea is to reduce the trauma. If you try to teach the child this sequence before the child is ready, then toilet training will be frustrating for both of you. If they are dry for three half hours in a row for half the days of the week then they are probably ready. Basically the child needs to demonstrate that there is some idea of a difference in having wet or dry pants before sucess will be achieved. A potty seat that fits over the regular toilet is preferable to a potty chair, as the regular toilet is what you want to eventually use.