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Refer below links for a complete jMeter tutorial.
ASP.NET Viewstate is a client-level state management implementation which tracks user state, it results in a dynamic parameter which travels back and forth from server to the client and vice versa.
If it prevents you from recording a JMeter test - you can use an alternative solution like JMeter Chrome Extension
But be aware that even after successful recording you won't be able to successfully replay your script as you will still need to handle this VIEWSTATE value so you will need to amend your Test Plan like:
See ASP.NET Login Testing with JMeter article for more information.