How do I make a RCA to VGA converter?
This is an advanced topic with high frequency signals. Basic IC knowledge won't get you there here I'm afraid.

You basically have two options:
- Get a multimedia SOC, like in TV's.
- Get multimedia decoders, from Analog Devices for example.

Both require niche parts that might be hard to acquire and implement.

I suggest you find a reinventing the wheel.

Note: VGA has two sync lines that component video has encoded into the signal. Although the signals are similar, functionality is not guaranteed.