You need to learn a programming language like Python, Ruby on Rails or C# + .net for example.
https://www.python.org/about/gettingstarted/
http://guides.rubyonrails.org/getting_started.html
https://www.microsoft.com/net/learn/in-browser-tutorial/1
For python specifically (as that's what I know about), you need to learn usage of some modules that will help in web automation, like requests, pycurl, json, etc.
You also need basic knowledge of the http protocol and some html, it will make things easier.
EDIT: If you don't want to learn all this, you can learn browser imacros (free), or even using a GUI bot making software (building bots of your own with the help of drag & drop) like Ubot Studio or Zenno Labs - those are great options for beginners, but they're paid software.