There is a huge amount of enzyme types in the human body. We have digestive enzymes such as pepsinogen, cardiac enzymes such as Trop-I, liver enzymes such as GGT. If you are curious of enzymes in the human body I suggest you look at specific systems or organs. An example would be to ask the internets about "pancreatic enzymes".
Enzymes are proteins that catalyze chemical reactions Although the enzymes themselves are incapable of regulating these reactions, the enzymes are self-regulated through mechanisms like feedback inhibition and competitive inhibition. Therefore, enzymes indirectly regulate the biochemical reactions which they catalyze
Enzymes have an active site that is specific for a substrate - therefore enzymes only work when the right substrate is present. The surfaces of the enzyme and the substrate fit together - like a lock and key - allowing the enzyme to fulfil its function. The theory of "induced fit" is more widely accepted - it is similar, but the enzyme shape changes to accommodate the substrate.