Question: how did the world start?

Stewart Martin-Haugh answered on 13 Nov 2018:

Everything we see in space is flying away from everything else. Space itself is expanding like a balloon. If you trace that back in time, it seems like everything must have been squeezed together into one point and then exploded outwards. We call that initial squeeze point the Big Bang.

We have a good theory for how things worked up to a few fractions of a second before the Big Bang. Before that, we don’t know how to do the calculations. And we don’t know what, if anything, came before the Big Bang.

After the Big Bang, particles joined together to form nuclei, then atoms, then molecules and eventually stars. Stars are very heavy and end up with a disk of matter orbiting around them. One of those stars was the Sun, and one of the disks collapsed into a set of planets. One of those planets was the Earth, and turned out to be in the right place for life to form.

A few billion years later, I answered your question on this website.