Red section should change the font of all text in the layer. Blue section is for fine tuning and will only work for the selected text.
The blue section doesn't have the font list button, but you can delete the font name in it and type in the first letters of the font you want to use and the list will pop-up.
Exercise: in "Example Text" select word "Example" and you can change it's size and font using the blue section.
It takes some experimenting but generally the red section is global for selected layer while the blue section is for fine tuning selected text.