Final answer:
The first step in changing an ostomy bag is to explain the procedure to the client to ensure understanding and provide reassurance.
Step-by-step explanation:
When caring for a client with an ostomy and changing the ostomy bag, the nurse aide should perform the following steps in order:
- Explain the procedure to the client to ensure they understand what will happen and to provide reassurance.
 - Wash hands thoroughly to prevent the spread of infection and maintain cleanliness.
 - Put on gloves to protect both the nurse aide and the client from potential contaminants.
 - Proceed with washing the area around the stoma once proper protective measures have been taken.
 
Therefore, the first step should be to explain the procedure to the client (C).