Why are some planets closer to the sun and some further away

Ok so it starts out

Sun

Mercury

Venus

Earth

Mars

Jupiter

Saturn

Uranus

Neptune

Pluto (If you want to still count it as a planet, but the planets now say it is not a large planet, but a dwarf planet. Just like some other main dwarf planets Eris, Ceres, MakeMake, and Haumea) (Pluto is not a planet for is does not meet all of the requirements to be an actual planet)