Hey guys. First of all… I’m a COMPLETE noob at Blender. This is literally my first day using it. Could someone tell me what’s being done at this part in this video? Modelling Toy Freddy (FNAF Fan Art) - YouTube
I see that he is somehow filling in the gaps there, but I have no idea how he’s doing it. If someone could tell me, that would be great. Thanks!
Hi Rapidworm! 
First off - thank you for your interest in learning Blender! Blender is an awsome program - my favourite, and there is a great 3D asset pipeline between Blender and UE4.
To answer your question straight up - The video guy is pressing “F” on the Keyboard, that stands for “Fill”. In Edit Mode in Blender “F” creates a Face between the selected Vertices or Edges.
I recommend that you start with the Basic Blender learning tutorials: https://www.youtube.com/watch?v=LLV7h-WLIx0
Goodluck and have fun learning Blender! 
Also if you have the time, read the documentation http://www.blender.org/manual/ thought it could be best… there is what it is (you can also use it as reference).
And if you ahve some spare money and want to support blender and learn in the way and have access to the projects they do for use it and promote it at the same time join https://cloud.blender.org/ (I did get a credit on the laundromat for been there :P).
Also there are a lot of free channels on youtube for blender like https://www.youtube.com/watch?v=lY6KPrc4uMw&list=PLda3VoSoc_TR7X7wfblBGiRz-bvhKpGkS
Blender is amazing.