Build a pressurized greenhouse. There may be plants that can be bred to stand the radiation, or to make it even easier, put them underground and either use electric light or bend sunlight in with mirrors. Water we can find if we dig for it.

"Terraforming" is highly oversold. It looks good in SF, when the techniques are basically "magic." We don't even know much about how our own planet's environment works, and making a lifeless world into a stable human-friendly environment is several steps past that.

It would be interesting to research the concept--you never know--but right now for what it would take to make Mars into an Earth-like world, I could fill the Solar System with O'Neill colonies, or saturate Mars with wondrous underground cities.