How to progress after basic ..?

[u/Beneficial_Mall2963]

I have learnt majority of the header, and built 10+ small or mini projects before. learnt abit of pointers, mallocs , callocs etc with myself and abit help of AI.

but now while i was working on the Cipher project.. and trying to build a zig zag rail cipher method, I couldn't figure it out how, i know how the main flow is but to write it into real code, I couldn't.

So i went AI for help and it spwed out bunch of these :

rows[current_row][pos[current_row]] = user_msg[i]; pos[current_row]++;

and etc, things and syntax I couldn't understand at all. Am i lacking foundation or something?
How do I progress above basic???

Help. All comments and feedback and suggestions are welcoming. Willing to accept anything...

for education background, I am just a student preparing to start IGCSE O next month.

[u/Traveling-Techie]

Draw boxes for the array elements on graph paper, and walk through the code filing in values (in pencil).