I have a I797 petition because I changed from a B2 to a H4 visa, Im going to my home country in Dec how do I apply at the Embassy there for stamping? do I just ,make a appointment? what do I need to take with? is there anything I need to fill in, before making a appointment?
You need to file Form DS-160, then pay the VISA fees and make appointment with your nearest consulate for interview. These are the basic things one who seeks non-immigrant visa should do.
From your other [question](http://redbus2us.com/qa/1435/do-i-fill-in-a-ds160-form-to-apply-for-status-change-b2-h4-stamp), I know that you will be going for VISA interview in South Africa - hence the following links point to information specific to that country.
US Embassy, South Africa - [Non-Immigrant Visas - How to Apply](http://southafrica.usembassy.gov/visas_niv_guide.html)
The Visa Information Service Center (VISC) - [The U.S. Visa Service](http://usvisa-info.com/en-ZA/selfservice/ss_country_welcome)