Newborn marsupials are bean sized, blind, earless/deaf and hairless. And for them to survive it is crucial that once they came out of the mother's womb they must crawl inside their mother's pouch and attach themselves in a nipple and the mother marsupial will nurse it's young. And the nursing will continue till the time that they're about the same size. 

During that process, once the young marsupial has fully developed they will be weaned by their mothers to prepare them on living a life of their own. The weaning process or also known as the training process lasts for a couple of months. The training includes how to survive on it's own, how to burrow if they're the burrowing type, grazing type or tree dwelling type (mainly, it depends on what kind or type of marsupial they are), how to look for water source and how to protect itself from predators.

After the training the young marsupials are ready to face the world on their own and are also ready for mating.

There are solitary marsupials and also "social" marsupials, that live groups of 2-4. Female marsupials species have different types of marsupial too. For example the wombat specie has a backwards-facing pouch and the koala has a downwards-facing with a drawstring like muscle.

The type of marsupium (pouch) a female marsupial has, depends on the lifestyle of the marsupial specie.