I am an Indian,I went on a trip to the US in the summer, after eating at a restaurant there,how many tip is it proper to give to a waiter?

The standard appropriate tip in the US is 15% of your total bill, before taxes or any surcharges. For really good service, a higher tip is appropriate and appreciated by the server. 

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One tip is usually sufficient.

You can't go wrong at 15%. You can get tip calculator applications installed on your cell phone for free. 

15% (before taxes)  is the standard advice prior to the pandemic   

Be aware in some states sales tax can be up 10%.