I have already read Way of Kings and Words of Radiance and I was wondering what I should read next. I heard there are six smaller books that I need to read before reading Oathbringer and have no idea what order to read them in.
There is only one book in between Words of Radiance and Oathbringer, Edgedancer. While not strictly necessary, it is recommended as it sets up some characters for Oathbringer a little better than otherwise. I'd probably also recommend Warbreaker since it crosses over quite heavily with Words of Radiance and Oathbringer.
As for these "six smaller books" I'm not really sure what you are a talking about. The Cosmere is an interconnected universe, so you could read any of them or none of them. It could be possible you are talking about the Arcanum Unbounded anthology which Edgedancer is also published in, but none of the other short stories relate to The Stormlight Archive in any meaningful way.
So in short, my recommended reading order for the best experience is:
Other than the main novels (Way of Kings, Words of Radiance and Oathbringer) the only other piece of fiction that's been published that's set on Roshar is Edgedancer, which is a novella that was part of Sanderson's Arcanum Unbounded collection.
The "six smaller books" may be referring to other works set in Sanderson's Cosmere. Minor spoilers ahead...
Many of Brandon's book series are set in a shared universe called the Cosmere. To date, these series are Mistborn, Warbreaker, Elantris, White Sand and Stormlight Archive.
It's not necessary to read any of the others in order to understand the events of the Stormlight books. However, there are characters from one series that appear in another. It's mostly minor characters, with a few notable exceptions. For example, Wit plays a significant role in most of the Cosmere stories. And I suspect that as each series continues, the cross-overs will become more prominent.
As for a reading order, I'd agree with amflare's recommendation if you're looking to stay mostly in the Stormlight world. However, if you're looking to branch out into the wider Cosmere, I'd recommend checking out the chart provided in this answer. It's a little out of date (Oathbringer is listed as forthcoming, for example). However, the starting points are still valid.