You have to hold the left mouse button to toss the bait at the lake, the longer you hold, more distant the bait goes into the pond.
When the fish bites the bait, it will glow blue and you have to left click to proceed to the next part of the mini-game.
Then, you have to hold the Left mouse button to raise the bar up and align it with the little fishy icon on display to catch the fish. If you stop holding the left button, the bar will go down.
PAY ATTENTION to the red sparkly fish running around and also the biggest fishes in the pond. Those are the most valuable ones.