Just the bulb. Open your owner's manual or the cover on the back side of the headlight pull out your burned out bulb and insert new one in the same way you take out the bad one. Try to do it without touching the glass part of the new bulb or use cotton gloves.
1999 ML320 230K miles
2003 Lexus GX470 285K miles
2001 ML320 162K miles
1980 280SE EURO W126 156K miles 142mph top speed SOLD
1984 300D TURBO DIESEL W123 SOLD