You will be able to play the basketball mini-game after completing Tagging Up Turf near the beginning of the game. There are a number of basketball courts in the game, where you can simply pick up the basketball there to start playing. While you have the basketball in your hands, press the button indicated on your screen to start Challenge Mode. A marker will appear and if you make a basket from that marker, you will score points. The biggest tip in making baskets is to release the button at the peak of your jump. You will be timed while playing basketball and as you score points, the marker will move around and the shots will become more challenging.
You need to score a total of 30 points in one session for this trophy/achievement, which can be a little challenging, since you only score 1 point for the first few shots, then 2 for all others. Some of the later shots can be tricky, though, since they are far from the basket and if you miss, you will need to run to pick the ball back up quickly to try another shot from the same spot. Also, it’s important to know that only the bigger courts will allow you to start the challenge, as the one outside Sweet’s house doesn’t work. There is one in Playa Del Seville, behind the barber shop, as well as another in East Los Santos.