making a contour map

Dear reader,

For an assignment i need to make a contour map of reservoir layer in a subsurface. I have been given a grid of x(35:1:48) and y(74:1:85) and on certain points a depth of my reservoir. To make a contour map I need to have values of depth on all the points of x and y. I think I need to interpolate, but I don't know how to do that. Can someone please help me?