Brief Explanation of Visas and Statuses

Visas are permission to enter the U.S. and are obtained outside the U.S.   In simple terms it allows a foreign national to seek entry into the U.S.
Immigrant Visas allow an individual to enter the U.S. as a Legal Permanent Resident and upon entry into the U.S., the individual becomes a Legal Permanent Resident, also known as a Green Card holder.
When a foreign national is legally admitted to the U.S., he acquires a Status.  Statuses are an individuals current immigration classification within the U.S.  These statuses may be able to be changed to another status depending on an individuals qualifications (i.e. non-immigrant status to non-immigrant status).  
An individual may also be able to adjust non-immigrant status to that of Legal Permanent Resident depending on qualifications.