Bound just means the direction. For example, "The south bound train on platform one departs in 10 minutes." South bound means 'heading south, or going southwards.''

It means you are on your way home.

It appears to originate from from boun 1200c meaning ready or intending to go forward. Then later the addition of towards the "bounds"(boundary borders) of your home, was added. one phrase two word "homeward bound" encapsulates "I am going or intending to go forward to my home towards the bounds of my home the borders of my home. That actually means "going home" You will still hear some speakers say "I am boun to forgot my keys" or similar sentences. Meaning I will most probably forget my keys. Some speakers will say "I am bound to forget my keys" = the same. Both using bound in a different contextual meaning.

The "-ward" part means "in the direction of". You probably know the words "forward" and "backward" already. "Bound" has a few meanings, and in this context (as an adjective) it means going, heading or moving. So, "homeward bound" means "moving in the direction of home".