instantiate objects every seconds

hi , how i can creating a number of enemy tanks ,for example every 10 seconds 1 tank from differnt places or positions and not at same time .

Check out Invoke or InvokeRepeating

The simplest way is to make a counter variable to which you will add Time.deltaTime every frame (so this would go inside an Update() method) and, when it reaches your number (in your case, 10) you set it to 0 and instantiate your tank.

Another way is with a Coroutine that contains a yield return new WaitForSeconds(10) sentence before spawning your tank. In this second case, I’m not sure about how it should be structured, though.