Your Gleason score is G8, made up of 4+4. The numbers indicate how distorted the cells are on a scale of 1-5 where 1 is completely normal and anything from 3 to 5 is cancer. The higher the number, the more aggressively the cancer could behave. The first number is the most common pattern and the second number is the second most common pattern so basically, the vast majority of the cancer cells in your samples were very distorted but not the worst.
The total (G7, G8, G10, etc) is used to predict how aggressive your cancer might be if not treated. A G8 is higher risk than G6 or G7.
The T2 indicates that the cancer is inside your prostate, can be seen on a scan or felt with a finger and probably hasn't burst out of the edge. Imagine your prostate is an orange ... T2 means that they believe the cancer is inside and can't be seen on the skin.
You will (should) get some more details; the fill diagnosis is usually written as G8(4+4) T2b N0 M0 or similar. T2a, T2b or T2c tells the doctors how much cancer there is inside the prostate. The N indicates whether or not the lymph nodes are affected and the M indicates whether there is spread to bones or other parts of the body.