most games engines let you write scripts or code. usually in a custom language, but sometimes a standard one like c#. when running, the game engine calls this code. this lets you modify the behavior of the engine (or define it in the first place).

writing a RPG of any significance in just month is a tall order unless you use an engine you don't have to mod, are skilled with it (2+ years experience), and only use pre-made assets. even then it would be very hard, and you would not sleep much. there's just so much to an rpg. first you need all the things a shooter has, levels and monsters and weapons and combat, then you need classes / skills / perks, magic / techno / artifacts, inventory systems, dialog systems, quest systems, the list goes on....

pong you can do in one man-month. skyrim is measured in hundreds of man-years (IE about 500 man-years to build skyrim: 100 people and 5 years. or about 2000*500 = 1,000,000 hours of labor - and that's just working 8 hours a day, 5 days a week, 50 weeks a year. you know the folks at bethesda (like all gamedevs) work longer hours than that.

at their best, a single dev can only average 15 hours a day after sleep, showers, meals, and bathroom stops - no work, no school, no family, no friends, no taking breaks - just game development. that's just 105 hours a week. or 5475 hours a year. while that's not bad compared to the ~2000 hours a year for a 9-5 with vacation, it would still take you 182 years to write skyrim. and that's only if writing skyrim was all you did except eat, shower, sh*t, and sleep. IE if you had no life.

very detailed! thank you