First you use 3 sticks and 2 string in a crafting table to get a fishing rod. Then you go to your designated fishing spot and press the 'Fish's button. Then you wait for particles in the water to reach your bobber. Then you press the 'Fish' button again to retract the bobber and hopefully get something. If you don't get anything, it is called a bug and should be reported.
I have noticed this as well. The little particles will come up to your bobber and then when you press the 'fish' button, the line returns but not any fish.
Bug is no longer present in 1.13.0.18