Any tutorials on getting started on making myself a mod?

I started watching the series by him, but like.... I guess I wanna go for the "more-complex" stuff like making a custom mission. (Custom Mission going by changing homer into someone else and having their own dialogue from the show) Or if I should start small, how do I something like edit the phonebooth so it has all the secret cars?

Or if I should start small, how do I something like edit the phonebooth so it has all the secret cars?

In order to do this, you would need to:

• Have a copy of the game's "rewards.mfk" file placed at \scripts\missions.
• Edit said rewards.mfk file and replace vehicles found within it with the bonus vehicles.
• Include Phone Booth art for said vehicles in \art\frontend\dynaload\images\cars2D (the naming format is "<vehicle name>.p3d" for the regular image and "<vehicle name>D.p3d" for the damaged image).