Almost all broadband ISPs give you more download bandwidth than upload bandwidth because the vast majority of Internet users download far more than they upload. Yes, they're both going over the same wire, but on different signals.
Latency is the amount of time that goes by between the instant your computer sends out a signal to the ISP or to a server computer, and the instant that signal is received by the ISP or the server computer. Signals do not go over the network instantaneously; they take a while to arrive at their destination. Latency tends to be especially bad with satellite broadband, because the signal has to go to a transmitter facility, get beamed up to a satellite 26,000 miles away, get beamed back down, and then get converted from a radio signal back into an electrical signal again.
What does latency actually mean? The longer the latency, the longer it will take between the time when you type a Web address in your address bar and the time the site starts to load. In games, it means that when you push the button to shoot your gun, your character will shoot a short time (or, if the latency is high, a long time) after you push the button. If you are using a Webcam, there will be a delay between when you do something and when the person on the other end sees it; there's a time lag in the picture.