hello all, im an 18yr old volvo user , i baught a volvo 850 GLE (automatic trans) with 80,000Km

i need to know how to read the codes, ive seen a link to a geocite site but i didnt understand weel waht should i do,
excuse me but im not an english native speaker and dont know the name of parts in english, but i can undersand when i read them.


the reason for this is that 2 weeks ago the volvo service shop change for me valve head or something , coz the transmition was not ingaging the 2nd gear, i payed for it ~1000$. yeterday i was driving and sudenly the car was slow to move from still and the arrow was flashing( iread its something about locked at 3rd gear) i turned it off then on 2 times then everything went ok.
i called the service and they told me its maybe moist on the wires.
but i need to read the codes that the computer stored and interpret them , any help is appreciated.
and any advice on caring for trans or other important things i should know.

note: im a power driver and sometimes i feel taht i over stress the car like fast takeovers and things like that ( when u trie to pass from behind a slow moving car :)) and i shift a lot (or i feel that) between D and 3