To attach a computer to the internet, you will need to have an internet connection in your home.
Your Dell inspiron desktop does not have a wireless connection card in it, unless you ordered that with your purchase. Unlike laptops, which mostly do have a Wifi card in it, to be more mobile.
After subscribing you will probably get a router to connect to your ISP (Internet Service Provider) something like this, sometimes the antenna's are inside (the antenna is for wireless connections):http://www.dlink.com/-/media/images/Products/DIR/803/DIR803A1ImageHBack.png
In the yellow port comes the internet connection from the modem, in the ports 1,2,3 and 4 you can connect internet capable devices, so also a desktop computer.
Then to get your computer connecting to the router you need to attach a so-called patch cable http://www.computercablestore.com/Certified_Cat_6_Patch_Boo_Blue_catID2175.aspx
to the router and to your computer in the network port: Sometimes the ISP gives one added to the package when you get your router.
Normally after booting up the computer will find the network automatically, else call the helpdesk of your internet provider or ask a computer knowledgable person to help you.
This is a Fibre Glass Modem on the right and next to it a router (left), the router can connect to your computer.