The first way-The unmoved mover
The universe is full od things in motion/change.-Movement is the change from potentiality to actuality.
An object only moves when an external froce is applied to it.-An oject cannot change itself.
Therefore there must be an unmoved mover which has been moved by nothing else, which is God.
Only an actual thing can change something from a potential thing to an actual thing.
Potential things cannot change anything.
Infinite regress is impossible.
The chain of moevements cannot go back forever because there would be no first mover, and consequently no other movers.(If the first domino never moved, none of the others would.
Infinity is impossible because there must have been a starting point-Aquinas would say there must be a prime mover which is unmoved, which is God.