HelpStarting a internal hack from scratch?

I've been looking around the internet for some knowledge about how to code a internal hack from scratch. But couldn't find what I was looking for. Also how they work and such. A point to a good direction would be great.

There are thousands of SDK's out there.
You could start by looking at:

MarkHC's latest framework
ViKiNGS Christmas SDK
de_stroyer
CSGO-Example
and many more.

Internal hacks are just like external hacks, just that you read memory by dereferencing the pointers directly.

If you want to get advanced, call the engine functions. To do that, you'd have to understand how the engine is built ( how do multiple modules communicate to eachother ), how you can utilize the engine, how classes are layed out in memory etc..