How did our bodies decide on the right enzymes and where did we get them?
I can understand why your asked this sort of question so I will clear your doubts one by one.

First of all Enzymes are not scattered inside our body, every enzyme is localised in a particular orgenelle or compartment of protoplasm in the cell, where they play their specific role.

Such as the enzymes of glycolysis ( the process by which you create ATP and breakdown glucose to pyruvate) are present in cytoplasm where as the enzymes for TCA ( Oxidative-decarboxylation of AcetylCoA) are present in mitochondria.

Enzymes are very specific.(1) If you have heard of lock and key hypothesis which states that an enzyme binds to the substrate that is complementary to its active site. Enzymes have very high specificity for their substrates the active site where reactions happen are somewhat complementary to the Enzyme substrate complex and thereby it provides the binding energy that lower downs the activation energy of that particular reactions that enzyme is going to catalyse.

I hope that helps!

References: (1) please refer to lehninger principles of biochemistry for further information!