Movements like the ones you mentioned tried to help farmers by pushing for regulation of businesses like the railroads and by trying to give the farmers more power in the market economy.
The Grange, for example, tried to get farmers to pool their resources and buy and sell cooperatively. If they would all buy together, they might get better deals from the firms that were selling things like fertilizer and plows.
As another example, both the Grange and the Populists pushed for regulation of railroad rates. They didn't want the railroads to be able to (in their eyes) overcharge farmers for hauling produce to market.
These movements, then, were generally aimed at trying to help the farmers to avoid being exploited by big businesses.
The Grange, the farmers' alliances, and the Populist Party tried to help farmers in several ways. The Grange tried to help farmers by providing educational and social events. Farmers would attend classes to learn about new farming techniques. They would attend social events to deal with the isolation the farmers faced.
The Grange and the farmers' alliances also worked to raise crop prices. They tried to pool their crops to help raise the price they got for them. They also tried to work with the railroads to get rebates on shipping their crops. However, they were unsuccessful in doing this.
The Populist Party worked to change financial policy in our country. They wanted a money supply based on gold and silver. This would lead to some inflation that would allow for the prices of crops to rise. The Populist Party also wanted to control the banks and the railroads. They felt the banks charged farmers higher interest rates than other businesses. They also felt that railroads discriminated against farmers by not giving them rebates like railroads gave to other businesses. They wanted to have the government control the banks and the railroad companies.