When my Ipad is connected thru USB to computer using Windows 7, it doesnt show in windows explorer
An iPad isn't designed to mount as a drive, it won't show in windows explorer unless you have photos on it that were taken with the iPad, copied to it via the camera connection kit, or were saved from emails/websites - if you do then it should show as a camera, allowing you to copy them off.
If you want to sync content to it then you need to use iTunes on your computer to so do. If you don't have iTunes installed then you can download it from here : http://www.apple.com/itunes/download/
If you haven't synced it to that computer before then you may find this page useful : https://discussions.apple.com/docs/DOC-3141
Syncing with iTunes : http://support.apple.com/kb/HT1386
Syncing media : http://support.apple.com/kb/HT1351
Syncing apps : http://support.apple.com/kb/PH12315
Syncing photos : http://support.apple.com/kb/HT4236