How to connect 3-digit display and suppress leading zeroes?
The most significant number (at least in Western writing) is the leftmost. Like the leftmost digit of your paycheck is more important than the ones to the right of it. 

Ripple blanking means that if the leftmost digit is a 0, it will be blanked, and its  /RBO  (ripple blanking output) will go low, indicating to the next most significant digit that it can blank if it is told to display a 0. This could ripple all the way down to the least significant digit. 

If all the digits are zeros, you probably want the least significant one to show a zero rather than all blank, so you tie the /RBI input to high (don't blank). 

The rules are a bit different if there's a decimal point in there, of course.