There are developer docs available by going to the first page of this forum (click on “community” at the top of the page) and then choose “developer documentation” at the top right there.
Before starting that though, you might want to take a look at this:
It should answer a lot of questions.
You can think of core (described at that link) like a scripting language for SmartThings, it may very well be all that you need.
If you do want to get into writing your own groovy code, I think the developer docs will be a good place to start, and then you can come back to this section of the forum as you have follow on questions.
