First cells are located where in the body?

When the sperm inpregnates the egg do they create one cell? Either way....when those cells start to divide and create a human, where do they end up in the human body once it is fully developed? Also there is something I was told about the human body recreating all the cells in your body over time....so are those cells dead and replaced after a time? Any info on this topic would really be appreciated...not sure if I should have posted in another forum or not so please let me know if there is a better place to post this question. THANK YOU SOOOO MUCH for your input on this!