Is it possible to make a Wi-Fi hotspot using Wi-Fi?

I need Internet on my computer but I don't have the Wi-Fi password on my computer, but my iPhone is logged in on the network. I don't know the password, so is there anyway I could create a Wi-Fi hotspot using the Wi-Fi on my iPhone? It's jailbroken too is that helps

Yes you can but check your data plan limits
http://www.gadgetreview.com/2011/09/how-to-turn-your-iphone-into-a-wifi-hotspot.html

So instead of finding out the password for the Wi-Fi that you already have you are trying to figure out how to use your iPhone as a hotspot. In general, adding more devices to the mix slow things down. You will get the best results if you hook your computer directly to your Wi-Fi network.

Your phone probably only had one Wi-Fi device. So it can either connect to Wi-Fi as a client, or act as a Wi-Fi hotspot to your mobile carrier network, but probably not both at the same time.