There's a statement called printf that is a little bit more advance to use.
Here is its syntax:
double number = 0.8123512512;
The console will display: 0.812
The % starts the whole thing, the 3 right after the period indicates that it only print out 3 decimal numbers, the "f" character stands for float type, which is kinda the same as double. The "number" after the comma stand for displaying the variable number in that blank.