The process of sponsoring your family member for lawful status in America will depend on your immigration status and if you are a US citizen, you can bring your spouse, parents, children and your siblings to the United States and if you are a Green Card holder, you can bring your spouse and your children to the United States. To help your family members to immigrate to America, you will have to file immigrant petitions for each relative you wish to bring to America. Hence, the first step is filing Form I-130, Petition for Alien Relative and this petition must be completed and signed by you as you are the sponsor. After you complete the form, you need to file it along with a proof of your relationship, proof of your citizenship status and the form filing fee.
As you are a US citizen, your immediate relatives need not wait for a long time to file petitions for immigrant visas as they can bypass the waiting lists and apply for immigrant visas as soon as you file From I-130. Your immediate relatives who can enjoy this benefit, are your parents, spouse and unmarried children. But the other family members will be placed on a waiting list and they can file applications for immigrant visas only after the USCIS approves the immigrant petition filed by you. After Form I-130 is approved, you will have to file Form I-864, Affidavit of Support and establish that you will financially support your family member. If you are Green Card holder, you can file petitions to sponsor your spouse and your children. There is no difference in the form filing process and you must file Form I-130 for each relative you wish to bring to America. However, the waiting time may differ and the relatives of US citizens will be given first priority and the relatives of Green Card holders will have to wait for a long time.
Similarly, you need to remember that, your relative must file an application for an immigrant visa only if he/she is in a foreign country while you file Form I-130. This process is called consular processing and this applies only to relatives who are abroad. If your immediate relative is in a foreign country, he/she must apply for an immigrant visa in a consular office in that foreign country and travel to America as a permanent resident after getting an immigrant visa. In this case, your immediate relatives can file for immigrant visas as soon as you file Form I-130 while the other relatives will have to wait until the USCIS approves Form I-130 and until immigrant visa numbers become available, to apply for immigrant visas.
The process may not be so complicated, if you are filing Form I-130 for your immediate relative who is a non-immigrant. In this case, your relative can file an application for adjustment of status and change his/her status to immigrant status and get a Green Card, while in America and Form I-485 for adjustment of status can be filed concurrently along with Form I-130. But this does not apply to the other categories of relatives and such relatives must wait until the immigrant petitions are approved and then file applications for adjustment of status.