(Disclaimer: I know very little about Windows, I Googled a bunch of stuff so the details might be wrong. Disassembly, if you want to follow along:
http://shell-storm.org/online/Online-Assembler-and-Disassemb...)
The program program is shellcode, so the first thing it does is set itself up with the state it needs. This includes clearing the direction flag, aligning the stack to 16 bytes, and figuring out where it is in memory (the call to 0xca both sticks an address on the stack and avoids some code described below). It then calls into a little subroutine (at 0xa) to read through the PEB → LoaderData → InMemoryOrderModuleList. The first entry is the entry for the main binary, from which it grabs the "FullDllName", does some sort of trivial hash on it, and compares it to a known value (presumably a check to see that it's running in a sane environment?) Then it largely skips the next entry (ntdll.dll) and goes to kernel32.dll, where it looks into the exports table to find what is presumably CreateProcessA (this is done using a similar hashing scheme, so the string is not directly present in the shellcode). There's a "calc.exe" string at the end of the code (perhaps you can spot it) and with that it has enough to pop a calc.