Ambient lighting is the overall lighting, where you use a warmer light in for example table lamps, pendants, recessed lights, uplights etc. to create a tranquil atmosphere.
When you are reading, cooking, fixing things or doing something else that requires your concentration, you need a more clear and downward directed light, so you can see what you are doing. This is referred to as task lighting or functional lighting and the sources used are often table lamps, but also floor lamps, wall lamps and pendants.
Back in the day, we chose our light bulbs based on the wattage. If we wanted a lot of light, we would buy a high wattage bulb. For less light, we would choose a lower wattage. Wattage is however, a unit of measure for energy use, and for a long time more energy meant more light. But, then new and more efficient lights bulbs, for example LEDs, came along and changed everything. In fact, lumens are the unit measure for light output. In other words, wattage is the amount of energy or electricity that the light bulb uses per hour. The higher the wattage, the more energy or electricity it consumes.