I want to get the key(send key) from user input how should I implement it?
driver.findElement(By.xpath(".//*[@id='vehicleNum']")).sendKeys("1121");
in input box what ever user type i want gen then i want to send through selenium?
Even your question is not clear properly but as I am assuming you need below solution. To get the input value from textbox, you can use below code:
driver.findElement(By.xpath(".//*[@id='vehicleNum']")).sendKeys("1121");
String str = driver.findElement(By.xpath(".//*[@id='vehicleNum']")).getAttribute("value");
System.out.println(str);
Program output will be "1121"