The position of equilibrium tells us how much product there is in the mixture. If the position shifts to the right, more products are made. If it shifts to the left, more reactants are present. When a condition is changed, the equilibrium shifts in the direction that opposes the change.
Temperature. Raising the temperature shifts the equilibrium in the endothermic direction. Lowering it shifts the equilibrium in the exothermic direction. The forward reaction that makes ammonia is exothermic, so raising the temperature reduces the amount of ammonia at equilibrium. A lower temperature gives a higher yield but a slower rate.
Pressure. Raising the pressure shifts the equilibrium towards the side with fewer gas molecules. In N2 + 3H2 ⇌ 2NH3 there are four gas molecules on the left and two on the right, so a higher pressure gives more ammonia.
Concentration. Increasing the concentration of a reactant shifts the equilibrium to the right, to use up the extra reactant. Removing a product, such as ammonia as it forms, also shifts the equilibrium to the right. A catalyst does not change the position of equilibrium.