The main way in which political machines built support for their candidates was by giving out favors of various sorts. They generally did not do as much of trying to convince people that their candidate had good policy positions as campaigns and parties do today. Instead, they saw voting for their candidate as something of a quid pro quo.
Political machines used their control over city government to amass large amounts of money. They did this largely by taking bribes and kickbacks and other such illegal money from people doing business in the city. They then used this money, in part, to do favors for their constituents. They would essentially run informal welfare services, giving money or food or other things to people in need. In exchange, the people were expected to vote for machine candidates.
Political machines also used their control over city government to allow them to give out jobs. In those days, all sorts of city jobs were given to political appointees, not to people hired based on their qualifications. This meant that the machines could give out all sorts of jobs (things like trash collection and maintenance) to their supporters. They would give jobs to the neighborhood machine leaders. The leaders would keep their jobs as long as they delivered enough votes from their neighborhoods. These leaders would be the ones giving out the “welfare” money and making sure the people voted the right way.
In other words, machine politics was a system in which the machines essentially bribed people to vote for them. They built support for candidates not by saying what the candidates believed but by giving help to people and requiring them to vote the “right” way in return.
They used their influence to build support for candidates. They bribed people (especially immigrants that need money the most), did favors, gave out jobs, etc. Political machines basically used anything that had to do with money to get support. They usually were corrupted and took money from the city for bribery.
An example of a political machine would be Boss Tweed in New York.