Define latitude and longitude. Use a sketch if you think it helpful. Latitude is the angle between a line drawn from a point on the surface of the earth to the center of the earth and the plane of the equator. Longitude of a point on the surface of the earth is the angle between the planes through the earth's axis and the point and the plane through Greenwich and the earth's axis. Density is the mass contained in a unit volume.
Continental crust is less dense.
Less dense materials float higher than more dense material so the continents tend to protrude further out of the mantle. Sketch the structure of the interior of the earth and identify four of the most important features. The crust, mantle and inner and outer core. The inner core is solid and the outer core is liquid. We know because the shear mode of seismic waves do not propagate through liquids though the pressure modes do.