What exactly does the collision theory state?

Collision theory states that if reactants have enough energy and are going at a certain speed, that when they collide, a chemical reaction will occur. There are some factors that affect collision theory, the most notable factor being temperature.

A higher temperature implies that the particles have more energy, meaning that will move faster. This gives them the right speed they need to react at. To be sure, a greater fraction of the molecules set about in a standard distribution will have the necessary kinetic energy to overcome the activation energy barrier.

Increasing the concentration of the reactants also affects the theory. If you have a higher concentration of reactants, it is more likely that the elements will react as there is a higher probability they will come into contact with each other.

Lastly, for gases, collision theory is also affected by pressure. Increasing the pressure gives the gas particles less space to move, hence once again having a higher probability of coming into contact with each other, I hope this helps!