The process of making an unearthly world more earth-like for purpose of supporting human life is called teraforming - Steven Wintergerst.
Teraforming Mars is only way we, humans can live and reproduce thus starting all over again on red planet. As stated above, teraforming transforms any world unlike Earth into an inhabitable place for humans. Of course we cannot convert another planet, Mars for example, 100% into Earth. However Mars must resemble Earth in following aspects: 1.Thicken small existing atmosphere and make it comprise important gases required for life, in their needed volume. 2.A new magnetosphere should be set up. A magnetosphere will protect inhabitants and every other object on Mars from being beamed with cosmic rays from outer space. All lives are in danger of being destroyed by cosmic rays as they may destroy DNA bonds of common life. 3.Make temperature more or less similar to that of Earth. As you know, Mars is colder than Earth as red planet is further away from sun that Earth is.
Some issues however cannot be changed. The main ones are: 1.Gravity of Mars is much lower than that of Earth. If ever humans settle there, they will have to cope with this. They will use much less effort to move about on Mars. But they will then be condemned to stay there unless they exercise regularly. This is simply because their muscles will become weaker and weaker and smaller and smaller in size. These muscles will not be able to cope with much larger effort needed to walk on Earth. 2.Mars is dead. They are no forests nor any bush. In fact there are no greens. Mars is forced to remain as this unless we re-melt its core (that’s a joke by way).
As written above, Mars has a small atmosphere and it should be prevented from completely vaporizing off. One proposed strategy to prevent vaporization is to put satellites around Mars but only just outside planet’s orbit. When satellites fly near atmosphere, they will pull thin atmosphere. When same satellites following their own orbit go further away from Mars, atmosphere will fall closer to planet thanks to Mars’s gravity. The latter has pulled its atmosphere back down. When this process is done over and over again, Martian atmosphere will thicken.
Another problem is a magnetosphere. A magnetosphere is a region of space surrounding in this case, Mars. The magnetosphere is thus dominated by object's magnetic field so that charged particles (found in cosmic rays) are trapped in it. Mars doesn’t have any such protection and we should try to set one up. Because I don’t have any extremely good ideas about how to solve this problem, what I am going to say may seem like science fiction but who knows… How about installing giant electromagnets in strategic places of Mars? These will act as a big magnet and this is exactly what magnetosphere is.