Peat pellets are an excellent propagation media and ideal for soil growers, they contain all the goodness your little seedling or cutting needs so you can just add water. Once new roots emerge from the pellet it can be repotted into a larger pot.
Peat pellets offer very high success rates and are ideal for potting on into larger soil based potting mixes.
Simply soak the dried pellet in water for 5-10 minutes until expanded into a useable peat starter block, put your seed/cutting into the top (open end) of the soaked pellet and place in the propagator.
Peat is a non-renewable resource so the conscientious gardener will avoid using it altogether or use it caringly and sparingly just for that initial rooting. Also, it is not typically recommended as a starter medium for hydroponics growers as similarly to soil peat contains decaying organic matter and micro-organisms.