Depending on where you look and who you ask you will get different answers for what a tempo run is.
A run at 85% to 90% of your maximum pace for a longer sustained period of time or on a scale from 0 - 10 an eight in effort depending on your fitness level. This is quite challenging and to be honest not recommend for beginners. First get your twenty minutes of running every second day in to get in the groove and start to like running and take it from there to speed up.
A run which starts at a very comfortable pace at the beginning and gradually gets faster until hitting the 8 of a 0 to 10 on your speed scale in the middle to then cool down again for the end. This is my preferred option of a tempo run as it is not as challenging as the first version of it. Try to arrange your run in a way that you have a nice stretch in the middle with good road conditioning to go full throttle and than gradually come back to your comfortable pace in the end.