it is an automatic only came on today goes off when u switch engine off

you have a switch on your shifter i believe for your Overdrive. You probably accidently bumped it, turning the overdrive off. Find your overdrive button and turn it back on.

overdrive. yes im a female but i really do know this one!

O/D is Overdrive. It is used automatically in cars. Normally you take it off when going down hills in order to slow you down without brakes or downshifting. There's a little button on your shift knob (automatic vehicles only) that turns it on/off. You may have accidentally pressed it.