Use your mouse to aim your shot, and once you've lined it up, hold down the left mouse button to gauge the power of your shot. Once you start charging up your shot, you can't change the direction it's moving in, so aim carefully, first.
Ballero is a combination between any golf game you've ever played and every puzzle game you've ever played. It's really easy when you start playing it, and you'll get the hang of it pretty quickly, but the harder levels get very hard, and the difficulty is something that will keep you coming back to this puzzle game over and over again.
First of all, the goal of every level is to connect three balls of the same color. Each level has a certain amount of balls you'll need to connect, and to connect these balls, you'll have to aim and shoot them so they get close enough (a distance that's shown on the top-left portion of the screen) and connect. There are five different difficulties to choose from, shown at the start of the game, and these range from rookie to expert. Each difficult will make the game that much harder by adding more balls to connect, obstacles to get in the way of levels, and shorter connecting distances.
If that didn't confuse you at all, then you'll be great at Ballero. If you've ever played any golf game before, then you'll know how to take a shot - just aim, then hold down the left mouse button and let go when you've reached the desired amount of power.
On harder difficulties of Ballero, there will even be more colors of balls to connect, more obstacles to get in your way, and shorter connecting distances. If you thought the first few levels of the game were difficult, then try out the last few levels - there are some where you'll have to connect up to 27 balls in one level.