PE file header hold a host of information, about the executable. The header preceeds the actual information of the file. In any windows executable file these day, the DOS header occupies the first 64 bytes of the file, it is present so that the program runs fine if loaded form DOS mode, then followed by PX header.
|Name||What it does|
|.text||Contains the actual excutable code|
|.rdata or .idata||Read only data for the program|
|.pdata||Only present in 64-bit|
|.rsrc||stores stuff needed by the programs aka resources|
Viewing PE files is simplified using tools like PEview.
Look at the Size of Raw Data and the Virtual Size, if you find that Virtual Size is insanely large that Size of Raw Data, you can safely assume that it is packed.(look in IMAGE_SECTION_HEADER .text ).