For questions specifically related to the RAMPS 1.6 controller board - The RepRap Arduino Mega Pololu Shield, or RAMPS for short, is an expansion shield for the Arduino Mega designed to fit the entire electronics for a RepRap 3D printer in a small, low cost package.
The RAMPS 1.6 is the second RAMPS iteration released by BIQU/BIGTREETECH. It replaces the original green power connector with a pair of screw terminals, adds a larger heatsink over the MOSFETS, and has a larger bed MOSFET. It maintains the surface-mounted fuses and flush MOSFETS of the RAMPS 1.5.
Also, the positions of the D1 and D2 diodes have been swapped from the positions in RAMPS 1.4, the D1 diode is now the diode closest to fuse F2. The same is true for RAMPS 1.5, also manufactured by BIQU/BIGTREETECH.
Additional information and a full list of features can be found at the RAMPS RepRap Wiki page.