There are a couple approaches that protection from radiation can take. You could pile up a few feet of dirt on top of your habitat. You could look for lava tubes to live in, which would be much bigger than earth due to the lower gravity. You could design your habitat to have an inner and outer shell that is filled with water, turning your water storage into radiation shielding. You could create an artificial magnetosphere by putting a satellite at the Lagrange point between Mars and the sun (estimates say 1GW of power going to a simple magnetic dipole could do this.) You could find a general cure for cancer and not worry about the radiation.

Radiation is scary but it’s not the instant death that popular media makes it out to be. Even if you did nothing to mitigate it and just lived your life on the surface of Mars it will only give you an increased risk of cancer over years of exposure. If you shipped in a bunch of 20-30 year olds and left them on the surface then they would probably be more likely than not to get cancer by the time they hit 80, but they wouldn’t just keel over and die after a couple years there.