Using secp256k1 in personal project
See here for an example of a #define configuration. You may then search for those macros in the repo to see their alternatives and define the relevant ones before you #include &quot;src/secp256k1.c&quot;

I can't seem to find any documentation or walkthrough guide on simple usage of the library

This library is not meant for use as a single header, as explained in the README.md:

Expose only higher level interfaces to minimize the API surface and improve application security. (&quot;Be difficult to use insecurely.&quot;)

The conventional way of using this library is compiling it and calling the linker when you compile your code with libsecp256k1.a for static linking (You may do gcc your-code.c libsecp256k1.a)
However, I used the library once with an #include only a long time ago, without any problems. That works, and as I described at the top, you just need a few #defines.
secp256k1.h is self-explanatory. You might want to read it all similarly to reading a story. Then you should be able to find the relevant functions.