oil on a 83 virago

how do you check the oil in a 83 virago how should the sight glass look on the center stand and should the bike be running
when i rode to day at low speeds the oil lighr would go on and off staying on for about 30 seconds to 1 min when i put the bike on the center stand the glass was half full not runningwhen it was running it was down to a quarter what kind of oil should i use