Simply put whats an API anyway?

API in robotic terms is  application programming interface which ofcourse doesn't make any sense. 

So to understand that in a simple way lets see what is a GUI, again in robotic terms its Graphic User Interface. i.e what ever action you want to take a button or something of the sort could be clicked. Like to close a browser you would take the mouse pointer to the x on the window. 

However if it was the end of your day and you were closing 20 such windows of various apps on your laptop, you know the pain of it. However if you could just automate it! 

Now imagine if there were 2000 such windows to be closed, you would want your computer do something about it but how will you tell your computer on what to do? This is were the APIs come into picture, they are a programatic way of doing manual things on computers. 

Basically APIs are a replacement for GUI if you want to automate a lot of stuff. 

Eg. 

If you are Google apps admin with no LDAP sync and etc and need to create users manually, on a day to day basis, you might be doing the below:-

First open a browser and go to your link, authenticate, go to admin console, then click on Add more users button and 

Select to enter user manually and then get the the fields to enter new user's name.

phew! all this to just reach the screen and what would be the plight if we had to enter 50 users on a given day!

APIs to our rescue!

by simply doing the prilimanaries you can put the below command and have the users created.

gam create user crashtestdummy firstname Crash lastname "Dummy" password "BuckleUp"!