Sponsoring a visa mean that your relative or friend will be sponsoring you financially for the trip. You can find more information about this topic here
If my family member or relative is a USA citizen:
It doesn’t make any difference if your relative is a citizen of the United States or not, even if he is a student or work there you will still have to follow the same procedure.
If I have an immediate family member i.e. Parents, siblings, spouse, children in United States who is a citizen:
If you want to visit your immediate family member like your son/daughter and he/she is the citizen of the United States then there are options to get their permanent visa (immigrant visa) however if they are only planning to visit you for a short period and you want to apply for visit visa only then again the process will be the same. Same process will be followed for spouse and parents.
For siblings brothers/sisters who are citizens, they can apply for immigrant visa’s (immigration to United States) for their brothers/sisters on their behalf but there is no specified time when they will get it, it may take 6 year or 10 years, no one can tell so if they want to visit you for a short period then they can apply for a visit visa however the process will remain the same for all B2 visas.
How will I mention that I am visiting my family member / friend / cousin etc in United States:
While filling the form you will need to mention the purpose of your visit which you will mention “I want to visit my uncle”. You will have to provide their contact details on the form including their name, address and contact number. This detail cannot make any difference in granting you a visit visa because if the visa consular will determine that you will not come back he/she will not grant you a visa.