Query regarding KEGG KGML pathway files
See the manual:

PPrel, in each of these, means protein-protein interaction, so we want to approach these by thinking about what the protein products of these genes can do with eachother.

For the first and second example, the subtype(s) give more information about the interaction. They aren't necessarily mutually exclusive. For example, phosphorylation can result in activation, inhibition, something else, or unknown. For the first one, there is phosphorylation and the effect is inhibition.  For the second one, the interaction is phosphorylation but the effect is not characterized.

When compound is under subtype for a PPrel relation, the value is the entry element ID for the compound (so go look for entry element 4), and it refers to an intermediate of two interacting proteins.