Question

How do the rockets burn or ingnite fuel in it,in space and accelerate?

Answer 1

Fire cannot burn without two critical elements: a fuel (the thing that burns) and an oxidizer (which starts theburning process and keeps it going). ... Many rockets carry a tank of liquid oxygen, which acts as the oxidizer needed to sustain the combustion reaction.

According to Netown's third law, every action has an equal and opposite reaction.

The combustion reaction gives a downward force and an equal upward thrust is obtained.

Thus the rocket moves upward.