You guys probably get this question a lot, but what do I do here? I’m trying to model some clothing on my character and the UI is a bit unfathomable. How do I fix the UI back to the default layout so I can create a mesh?
If that little grey patch between his feet is the default view grid floor, then your model is huge because that grid is about 16 meters square. Try scaling your model down and see if things don’t look more familiar 
From the model’s left foot look to the right and down. See that little + sign? Click it. Now go all the way over to the bottom left corner most icon on your screen and click it. A menu will pop up. Choose ‘Info’ (you are in ‘file browser’ mistakenly). (BTW, you can also do this with the icon in the very top right of the screen.) Now you should be back in familiar territory.
If you have some time look through the first few sections here. It’s easy to get lost in the interface of a powerful program without a guide.
Your model needs to wear more sunscreen.
Blender’s UI is extensively customizable. The manual sections most relevant to you are here and here.
To get back with the default UI layout and use the blend you had, try this :
- Launch Blender, click on File -> Load Factory Settings
- Click on File -> Open , then in the bottom right , disable “Load UI”
- Load the blend
Now if you have a custom layout you want to keep, just launch blender then
- Click on File -> Open , then in the bottom left , disable “Load UI”
- Load the blend
You can disable “Load UI” for each time you’ll launch Blender by going to File -> User PReferences -> File panel and disable “Load UI” , then on the bottom left click on “Save User Settings”