API's

Hello All,

Just read Bob's "10 Bad programming practices in RPGIV" I am happy to say I was 
only doing one (*INKn) which with the help of the /COPY Fkeys he mentioned 
(thanks Bob) I shall now stop. :-)  I have never used the B data type or even 
seen it used, but the reason for this post is where do I find out about API's? 
I have obviously seen them used and even used a couple (borrowed from someone 
else's code) but in my New Years mode and currently I am on a "lets learn 
something new" kick I would like to know more about these things. And also, so 
as not to get in Bob's bad books, I just need links, etc. not training on this 
forum (though a few pointers won't go amiss, but don't tell Bob.  ;-) )

Steve