Libraries - Where would I find a description of library calls

where find descriptions of library calls?  have sketch with......
#include <esp8266wifi.h>
#include <esp8266mdns.h>
#include <wificlient.h>
the sketch modified activates various relays via wifi using simple html addressing.  sketch goes sleep , unresponsive wifi calls.  not asking diagnose wifi issue.  need know where find plain english description of each library function call within each of above xxxx.h #include libraries.  need description of sent , returned (or void) every function in these libraries.   i can decipher library function calls in sketch, need know other functions available in these libraries, might make sketch more fault tolerant.  (and where) file extension for....  possibly .txt  file??   even more confusing can't fine either of esp8266 librareies on hard drive, yet sketch works. 

i purchased 1 of large arduino kits , worked lessons several books, function calls described, accept them on blind faith, add libraries ide , works flawlessly, can find  library function calls described.

the files on hard drive.  don't know did or went wrong.

the location of documentation depends upon library, place start comments in .h , .cpp files.  these files deciphering how functions work , functions available.

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