Reagan's domestic agenda marked a sharp break with the New Deal consensus that had reigned in the United States since the election of Franklin Delano Roosevelt in 1932. Roosevelt had ushered in an era of government growth. Since his time, it had been understood that the federal government was a positive source of good in people's life. Its role was to use its power to ensure general welfare. Roosevelt brought such programs as Social Security and unemployment insurance into being. He fought for and won baseline regulations including minimum wage and protection of children under 14 from paid labor.
After him, presidents both Republican and Democrat, continued his policies of using the government to make life better for people. Programs such as the GI bill (which paid for returning World War II veterans to attend college), Eisenhower's massive highway building program, Johsnon's Great Society (which included Medicare), and Nixon's creation of the EPA all improved the life and well-being of the average person.
Under Reagan that changed. Reagan believed that government was a problem that interfered with people's pursuit of the good life. He wanted to get rid of as many regulations and programs as possible in order to make government small enough to "drown in the bathtub." He argued that lower taxes would put money into people's pockets and help more than the programs the taxes supported. He believed that the for-profit business sector would be far more efficient at running the economy than the government sector and do a better job at ensuring a prosperous society for all. He cut taxes, especially on the wealthy. He cut regulations as much as possible. He tried as far as possible to free the business sector from government oversight. He did not expand government except for a massive increase in defense spending.
As for his social policies, he showed little interest in affirmative action programs and has been criticizing for ignoring the AIDS crisis that especially afflicted gay men. However, his AIDS policy (or lack thereof) was consistent with his conservative, pro-evangelical Christian social agenda.
All of this reflects Reagan's underlying ideology. Although he actually did not fully undo the New Deal welfare state, he set the groundwork for subsequent presidents to chip away at its foundations. Reagan's beliefs mirror those of Hoover and other pre-New Deal conservatives. Reagan wanted to go back to the time before Roosevelt came into office. Then, the federal government was much smaller. It interpreted the federal role primarily as supporting a defense department so that the country would be prepared for war. The other role of the federal government was to enforce existing federal laws. Social welfare was thought to be the responsibility of the states. Although there were some federal regulations, before the New Deal, business was largely left alone to operate as it saw fit.
Reagan supported his ideology, as said above, with massive tax cuts and large increases in defense spending, as well as as much regulation cutting as possible. Reagan knew his combination of tax cuts and defense increases would vastly increase deficits, but that did not bother him: it would provide the rationale down the road for cutting government social welfare spending.