Currently I do not have ground in my house wiring. I am planing to install ground wiring but the floor around the main service panel is cemented and I don't think I can place a ground rod in the floor. There is an iron rod sticking horizontally out of the wall behind where my main service panel is(main service panel is in the garage). There is a wire wrapped around that rod, which seems to be made out of steel, going into the ground. I think it was installed when the house was built (1968). can I connect the ground wire to that rod?
To meet current NEC codes you cannot have neutral and ground share the same grounding rod. Ground requires its own separate rod from each panel and sub-panel installed in the house.
The depth of the rod outside depends heavily on your area as factors like precipitation, soil composition and climate affect just how far the rod needs to be placed into the ground. Performing this work likely requires that you obtain a permit from your local municipality, meaning that you will need to have an inspection anyway. I would ask the inspector what he will be looking for in a ground rod.