on the lower right side - the butterfly is your oil fill and inspection, square head plug below that is the oil drain. typically you fill to base of fill hole, as stated above use compressor oil or ND 30. the funnel looking thing is the air intake clean it and replace element if it even has one - or best would be to replace with modern paper style filter head inlet will be pipe thread. remove the four head bolts and remove the valve plate, it will have reeds on both sides clean plate check for flatness and replace reeds. parts are easily found online just Google: ingersoll compressor parts, gaskets, reeds, filter, etc....