Starting Blocks for Sprinters
Starting blocks are reasonably simple devices. They have spikes that stick into the track and to pads, upon which the sprinter places their feet. They then push against these pads to get a powerful start in the direction of running, as opposed to pushing off the floor which involves a lot of vertical push and is therefore slower.
When buying blocks, basically, the more you spend the better the blocks you get are.
You don't need a hugely expensive set as a beginner / youngster as the amount of power that you are likely to be able to put on them as you start is not going be huge. The more expensive blocks are better build and heavier and are therefore a little more important to get if you are very strong and able to put a lot of pressure on them.
Championship blocks (which you don't need for practice!) have sensors in the pads to show whether or not athletes have done a false start or not.
When choosing blocks it is very important that they are as versatile as possible in terms of your being able to adjust the block positions and also the angle at which they tilt up.
Most blocks these days do this, but not all - this normally has about 20 positions for the former and 4 for the latter. You will find as you progress you probably will wish to alter the positions from which you push.
Some of the very cheap (often blue!) ones in the past didn't do this and were very limited in their use.
For more information on how to use blocks and make a great start to your sprint races see Block Starts