Handmade hero, assumes that you already know a little bit how to program. There is an introduction to C in the first week, but it can be hard if you've never programmed at all.
The series covers some common algorithms (sorting, hashing, random numbers, rendering...), data structures (link lists, hash tables, command buffers, free lists, voxels...) and Casey explains his way of designing API and what he consider good or bad APIs. In general the series shows you how you would work out problem so you can learn yourself.
If you're absolutely starting, you might want to find an introduction to C first and practice a little before watching handmade hero. You may also start by watching the intro to C videos and see it you can follow along. Note that you can use any text editor and that Casey doesn't use emacs anymore.
Also Casey is working on a beginner course but it's not out yet and won't be free.
I am waiting for starcode galaxy so hard. And now hearing that its not free I'm even more excited. I have been thinking that there are so many bad "courses" on the internet charging obscene amounts to teach things I can read in documentations and know them better than the person teaching it, and HMH is just free... it makes no sense.
You mentioned somewhere that he uses his own editor outside of HMH. He wrote his own editor? Is that available somewhere to purchase? Although, I think I'm too used to vim to ever switch to emacs now and I think he would have probably made something similar to emacs...
In handmade hero, Casey started with emacs, than switched to 4coder. In some stream he mentioned that outside of streaming he uses his own editor but as far as I know it's not available and probably never will be.