Have just bought an i-Pad Wi-Fi Cellular and cannot connect to any network, any ideas ?

Totally new and inexperienced to i-pads but have bought one as I need to travel but keep in touch with various things. Have put sim card in and it's asking me to activate i-Pad and offering networks or use mobile connection. As it's a cellular i-Pad I've tried mobile connection but nothing happens, what am I doing wrong ? There are no instructions in box to help.

If anyone can help I would be grateful.

Thanks in advance.

Steve.................