Application development starter kit for C programmer

I just know C and stdc.

I want to development an GUI-based application specifically for UNIX/Linux systems (atleast for now). Suggest me a list of things that I need to learn (like what GUI library I should use, what tool to use for compiling configuration, etc). Keep the list minimal (as I'm learning, I want to know what are the difficulties that occur using those minimal things, and then want to know how other tools solve those problems).