Virtual Users are created to Analyze the system Response 
under loads.

Vusers is nothing but simulating with the Real Time Users.

To conduct performance testing manually, it is not possible 
due to lack of resources in company, cooperation between 
test engineers and repeatability of that tests for that 
test engineers are using tools for performance testing.

To apply load on build vusers are creating, instead of real 
users the vuser created and our build feels it is 
operations as real users. 

if anything pls, let me know.