Assumptions: You have a valid Amazon account in your region and your account, PC and Kindle are all correctly registered to THAT Amazon account in THAT region.
1 - If your kindle is set up to connect with your home or local Wi-Fi service then you simply turn on the kindle, turn on wifi and tap a book cover or title - that book will download to your kindle. Once it has downloaded it is on your Kindle. You do not need wi-fi to read that book.
2 - If your kindle is not set up for wi-fi service (this is a bad, bad thing - think about setting it up if you can) then when you download an Amazon book to your laptop YOU MUST SET THAT DOWNLOAD AS DOWNLOAD AND TRANSFER VIA PC. You then connect your pc/laptop to your Kindle using the USB/Micro usb cable you use to charge the Kindle anyway and drag and drop those books from your laptop to your Kindle. The import part is to download with the setting TRANSFER VIA PC. The books can not be read on the pc, they can only be read on your Kindle.
SYNCHRONIZATION does very little on Amazon kindle/Fire devices - generally it just updates notes and last page read. it does NOT update books on devices.
I will try to find the quick link for how to drag and drop books, but you say that Wi-Fi is there so why you are not using it I am a little unclear about :(