Nexus 7 doesn't have sdcard folder when connected to PC I've just bought a Nexus 7. When I plugged it into my laptop, it shows the media folder, I'd like to access the sdcard folder just like the other devices. How to transfer files? 

I think "adb push" is not a good choice.
Nexus 7 doesn't support UMS (USB Mass Storage) out of box. But, it supports file transfer by MTP (Media Transfer Protocol). MTP allows you to push and pull any type of files from sdcard, but it doesn't allow you to edit files directly on sdcard (like you do with UMS mode).

From your screenshot, it looks like your Nexus 7 is connected with PTP (Photo Transfer Protocol), also known as Camera Mode. Switch to MTP mode and do whatever you want. Also make sure your PC OS supports MTP.