An immigrant, or resident, visa is the visa issued to a person with permission to live in the United States.
The majority of immigrant visas, including that for siblings, must be filed in the US. For some visas (spouse, minor child, and parent) the petition may be filed in Caracas, Venezuela. For more information on immigrant visas, please see United States Citizenship and Immigration Services.
Once you have received the requirements for the immigrant visa, and you meet all the requirements to apply in Caracas, Venezuela, please see "How to Apply for an Immigrant Visa ?"