Short answers, pulled from the story.
Mars to Stay is a mission architecture that proposes sending astronauts to Mars with the intention of remaining there permanently rather than returning to Earth. Advocates argue that eliminating the return trip drastically reduces cost and ensures a settlement takes root rather than just a brief visit.
The earliest formal outline of a Mars to Stay mission architecture was presented by George Herbert at the Case for Mars VI Workshop in 1996, in a talk titled "One Way to Mars." Space activist Bruce Mackenzie made a similar proposal at the 1998 International Space Development Conference.
Aldrin proposed recruiting pioneers at age 30, training them through age 35, then having them develop underground Martian habitats from age 35 to 65, at which point they could choose to return to Earth or remain. In August 2015, working with the Florida Institute of Technology, he presented a master plan to NASA for astronauts to serve ten-year tours and establish a colony before the year 2040.
Mars One, the Dutch not-for-profit founded by Bas Lansdorp, planned to land four permanent settlers on Mars in 2027 and relied on a reality television show, participant fees, and donations for funding. The financial model did not materialize at the needed scale, and on the 15th of January 2019 a court ordered the organization liquidated, sending it into bankruptcy administration.
The primary risks are radiation exposure and the effects of low gravity. Mars gravity is 38 percent of Earth's, and long-term human viability at that level remains a working assumption since no human has lived there. Robert Zubrin argued in Mars Direct that cancer increases for space-based astronauts are marginal and that near-total recovery of muscles and immune function is expected once settlers reach the Martian surface.
Robert Zubrin identified two main sources of economic value. Mars may contain concentrated metal deposits equal to or more valuable than silver that have never been extracted. Deuterium, a fuel essential to nuclear fusion power, is five times more concentrated on Mars than on Earth. Zubrin also argued that the scarcity of labor on Mars would drive high wages and spur technological and social advancement.