Visual Approach Edit
A visual approach is mostly used by VFR pilots, as they do not have the proper equipment to set up an autopilot for their aircraft. The visual approach is basically used on moderate to clear weather, as the pilot is controlling the entire approach. When doing an approach, the pilot also checks for VASI/PAPI lights, on the left or right side of the runway (usually on the left).
ILS Approach Edit
An Instrumental Landing System (ILS) approach is mostly used by IFR pilots. The aircraft must have an autopilot system to do an ILS approach. ILS approaches are usually done in from very foggy weather, to IFR only areas (due to weather), and sometimes when pilots just want to practice it.