The brief way to describe this is to say that Ronald Reagan wanted there to be lower taxes. He wanted the government to make fewer laws regulating what companies could do. Finally, he wanted to cut government funding to various types of social programs.
Pres. Reagan wanted to do these things because he was a conservatives. Conservatives, in general, want there to be less government. They especially think that the government should not regulate businesses -- they do not like minimum wage laws, for example. Conservatives also thing that social programs like welfare should be reduced so that people would have to find work instead of being able to live off government help.