Here "feet" represents Christ's lordship, authority, and power. The abstract noun "subjection" can be translated using the adjective "subject." Alternate translation: "put all things under Christ's power" "make all things subject to Christ" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-abstractnouns]])
Here "head" refers to the leader or the one who is in charge. Alternate translation: "ruler over all things" (See: [[rc://en/ta/man/translate/figs-metaphor]])