If your project includes a task for "Placing a order" at a supplier, this also may include that you need to take into account a delivery duration or waiting time.
This article describes how you can model this process, using a "lag".
An alternative possibility is to insert a delivery tasks, with a duration equal to the expected delivery time, in combination with setting the "Auto-complete" feature of a (long-duration) task.
See the first attachment "Modeling Delivery Tasks".
The second attachment covers some possibilities that you can consider for modeling supplier tasks.