If the user extracting is a “ordinary” user, the files will be owned by that user (by default).
If the user extracting is a super user, then the files ownership will be preserved (by default).

Note: This is by default and can be overridden when needed:

From the manual page of tar:

--same-owner
       try extracting files with the same ownership as exists in the archive (default for superuser)
 
--no-same-owner
       extract files as yourself (default for ordinary users)

By default untaring will put the contents into the current directory.
Sometimes it is not desirable to change directory to the target (such as in a scrip).

tar -xvvf /source/tarfile.tar -C /target

This will extract(x), very verbosly(vv) the file(f) /source/tarfile.tar to the directory(-C) /target (it will change the output folder to /target (so make sure it exists).