Lightroom day 2

Day one with lightroom 
I'm a bit lost. I just figured out the mobile part of Lr. The processing part is familiar, I have seen several processing tutorials on YouTube to know just about what's what. Its more detailed than aperture but that's about it. 

My questionning comes from what happens to the files when you're done with the processing. What happens when you send a dng file of 12-15mb that becomes a 90 something file after it passes through nik and becomes a tiff.