I don't know anything about PE files, never heard of them. However a "header" is some data that appears at or near the beginning of a file. A "section" is a part of a file which can be treated as a unit (sort of like the "sections" you get when you peel an orange).
Well, if I'm not mistaken, PE is the file format for windows NT executables. Sections are parts of the file that describe either code or different types of data. Sections have different permissions or attributes associated with them.
Looks like you are looking at word.exe. The Image Info describes the header for the EXE file - if you open word.exe with a hex editor you can find the same information in the first X bytes (I used to know what X was, 128? 256? but don't recall). And EXE (and a DLL) file are divided up into various sections into which different things are placed. Things such as the opcodes, text strings and images used by the program.
Go to the MSDN web site, there should be documentation there on how an EXE/DLL file is laid out.