What is Feature Barcoding technology? I heard the term Feature Barcoding a lot so I find resources to understand it. I have read docs of 10xgenomics and I see that Feature Barcoding technology is a method for adding extra channels of information to cells by running single-cell gene expression in parallel with other assays, this technology also do something with t-SNE and something with matrices. 

I can't imagine the whole picture because I don't know what are those adding extra channels of information to cells, single-cell gene expression and parallel with other assays mean. And what is the input and output of this technology? Is there any paper go along with this technology?
"Feature Barcoding" refers to using antibodies linked to specific oligos. The antibodies can then bind to cell surface markers of interest and the oligos they're conjugated with turned into normal scRNA-seq reads. This effectively means you can get a FACs profile for each cell without needing to run it through a FACs sorter and individually label it.

The "feature barcoding" nomenclature comes from 10X I think, but there are a few similar protocols (maybe they're exactly the same in the end, I'm not sure about the details) such as CITE-seq and REAP-seq. You can see a talk from 10X on this here.