I have Dell Inspiron 1525 with SIM slot behaind the battery, but I did not know how I can use it?for what it can be used? i put SIM card in it but nothing happened.
You need a WWAN card supported by one of the broadband cell providers that uses GSM-GPRS-HSPDA (AT&T or T-mobile in the US), and then you'll need a SIM card from the provider that is activated on your cellular contract. You also need, of course, a broadband data contract with your provider (somewhere around $60/month above your voice plan).
The SIM card alone is useless.