This image was taken from the International Space Station and displays the most important feature of the sun for life on Earth: Its light and heat!
The Sun is a spectral type G2 V dwarf star that emits 3.8 x 1033 ergs/sec or 3.8 x 1026 watts of electromagnetic power from gamma ray to radio wavelengths, with most of the energy emitted in the visible light spectrum between 400 nanometers and 800 nanometers. This is illustrated by the spectrum provided by Nick84 [CC BY-SA 3.0(link is external)], via Wikimedia Commons.
This is the spectrum seen at Earth’s surface where molecules of water vapor and carbon dioxide obscure some of the radiation to form the various dips in solar intensity. The common measure of solar brightness is called Irradiance. It represents the amount of energy (watts) that pass through a 1-meter2 surface facing the sun, and measured over a 1 nanometer bandwidth. Earth is located 150 million km from the sun, so if you surround the sun with a spherical surface with this radius, the surface area is A = 4piD2 or 2,8×1023 meters2. If we divide the solar luminosity by A we get 3.8×1026 watts/2.8×1023 m2 = 1,344 watts/m2 at the top of Earth’s atmosphere. Most of this is emitted in the spectrum between 300 to 900 nm for a 600 nm bandwidth, so the average irradiance over this spectral window is 1,344/600nm = 2.2 watts/m2/nm., which more or less matches the vertical axis of the above plot.
In one hour, or 3600 seconds, the sun produces 3.8×1026 joules/sec x 3600 sec = 1.4 x 1030 Joules of energy or 3.8 x 1023 kilowatt-hours.
Since E = mc2, and c = 3×108 m/s, in 1 hour the sun looses (1.4 x 1030 ergs)/(9 x 1016) = 1.5 x 1013 kilograms or 15 billion metric tons of mass each hour. It’s been doing this for about 4.5 billion years! So its mass loss over this time (3.9×1013 hours) = 5.9×1026 kg . But the sun’s mass is 2×1030 kg, so it has only lost about 0.0003 or 0.05% of its mass so far.