Engineering greenhouses on Mars is not an easy feat. The greenhouses would have to be 

built with an insulated material in order to regulate the internal temperature of the greenhouse. Additionally we would also need a material strong enough to keep out any unwanted radiation. Those materials would also be able to be used for the houses of the inhabitants. Keeping out radiation would help keep the inhabitants healthy. Another factor in keeping the inhabitants healthy would be our food production. Using the greenhouses we would be able to plant crops to feed the population. These greenhouses must be well kept and the crops must be nurtured well. Additionally advances in technology would also enable the extraction of oxygen from Mars' carbon dioxide. With the extraction of oxygen other life forms would be able to live there. Another way would be terraforming Mars. Terraforming Mars would also affect the atmosphere, making it more suitable for humans and other life forms.