Doctoral (Ph.D.) programs are a part of the Graduate School. These programs are very competetive and some offer financial aid, while some do not.
You will want to begin with:
Next you will want to go straight to your department for information about applying and special requiements. Some programs require the GRE and some do not. You must follow the instructions for each individual department.
Finally, you will want to explore cost and funding opportunities.
If you have questions about your program of study it is best to contact the department directly.