Download the official Build Instruction Document from 3DPrinterCzar and follow the steps . It claims the estimated building time at 3 hours but if you never done it before it will take longer. It took me 8 hours and that’s only the mechanical assembly. The document ended at 16 pages and was missing the next step-connecting all the wires between the motors, RAMPS, endstops and extruder.
You can use the RAMPS Wiring Guide for their Prusa i3 model but disregard the mentions of two Z-motors and two extruder motors – your Rostock Mini only have one of each !
You can also disregard connecting the LCD controller as it is not included.