The three main functions of railroads in the west is that they provided jobs, transportation, and sped the sale of products in the industrial North.
Building railroads created many jobs for immigrants and those who were just looking for work. They pay was extremely low, but they were jobs.
Once towns were settled, railroads were able to transport people for the first time, cutting a three month journey into one that took only a few days. This sped colonization in the west.
Lastly, people were able to sell much more. Farmers in the west had to spend months to sell their products in the north because they had to travel there by foot. Trains, however, could now buy livestock and grain and quickly get them to industrial america, which helped the farmers make a living wage, and fed the entire country.