[jcatha1]

Hi, I'm not very techie so I'm hoping someone can help me. Thanks in advance.
I bought one of these because I thought it would boost my poor Wi-Fi signal in some parts of the house. Is that what it's supposed to do, or have I made a mistake?
As it plugs into the main, where does the cable come into it? If it's got to be attached to my computer, it won't work as it's downstairs where the signal is bad and upstairs where my PC is!

Can anyone give me an idiots guide on this please?

Thanks