differentiation 0 Newbie Poster

Hi,
I've been playing a game from a few years back (I really enjoyed it) and I found that it was open source on github. I would love to make my own version and see how it goes. I have experience with python as a hobby, and I've had a go at c++ - I made a few games with the sdl library. The github link - https://github.com/id-Software/RTCW-SP
It will be great if I could at least render a level and a character. From what I see, the source has everything I need apart from the graphics.
If someone can give some pointers on what will be required and where to start I will be happy to hear :)
Here's a video of the gameplay - https://www.youtube.com/watch?v=FddW6VjFHAY