How can I use the sim slot

First, not every 6930 has a WWAN adapter, and even those without have the SIM slot. If your 6930 came with a WWAN adapter, there is an extra sticker behind the battery, next to the main label, indicating the type of WWAN adapter installed and the IMEI number.

If you have the WWAN adapter, the rest depends on the operating system.

For most Windows versions, you either have received a driver CD; if not, look on the HP website for WWAN drivers.

Under Linux, things get a bit hacky, as the un2400 adapter requires a binary firmware blob that you would need to extract from the Windows driver, as I’m not aware of any Linux distro shipping it. Unfortunately, in my own experience, I never got it to work under Linux.