Ancient peoples have been making glue from sap, vegetables and charcoal for thousands of years. There are many different formulations. -Before that, I would guess they had no easy ways of joining things.
Yes, many people do.
You can use white glue or super glue as well.
Either use a hot glue gun or some super glue.
No, you cannot use a solder gun as a hot glue gun.No, you cannot use a solder gun as a hot glue gun.
If the glue was a good glue then you will damage the wood before the glue lets go. Glue goes into the pores of the wood and holds tight. Usually to separate the two pieces you would need to saw them apart. This would give you a smoother separation.
They didn't. You can't use something BEFORE it is invented.
benches
bikes
Buttons.
pickaxes
carriages
People who do it usually use glue sticks or Aleenes glue.
You can glue things faster and more easily with a glue gun than with a tube of glue (although I still use tubes, personally).
horses or their feet.
wall sockets
Brief case
Buttons and knots.