In order to create a placement, you need to set up the placement details. 

To set up the placement

  1. Navigate to the Basic tab.

Basic tab — Add Placement

  1. On the Basic tab, to set up your placement, perform the following actions:
    1. Type your placement name and the placement identifier.
    2. Click the Select a Network list box to select an ad network.
      Note 
      An ad network collects the unsold ad inventory from multiple publishers and offers them to advertisers.
      Each network has a different tag generation process and serves ads in a unique way.
      Tip
      You can quickly find the required network by typing the network name on the Select a Network list box.
    3. Select the Platform checkbox to create tags. You can create a tag for:
      1. In-App (MRAID 2.0) - Tags to run over applications 
      2. Web - Standard tags to run over the web
        Note
        When you select Web as a platform, the Supports iframe option appear.
        Creative format such as Desktop TruSkin does not work in an iframe. 
    4. Click the Include Close Button option for interstitial creatives.
      Note
      An interstitial creative comes with a button to close the creative. When you select the No option, you can hide the close button.
    5. Select the Protocol option to specify the protocol.
      Note
      If a non-secure creative is served on a secure site, it can prompt a warning message, create ad serving problems, or even block the creative.
    6. Type the stack order value in the Z-Index box.
      Note 
      z-index is a CSS property to set the stack order of a creative element in a web page. Higher stack order number ensures creative element to appear before an element with a lower one.

Click Continue to save the details.

Friendly iframe is a mechanism whereby the tag is rendered within an iframe container. This ensures that any changes made by the creative do not impact the publisher or vice versa.

Iframe busting is applicable for expandable formats where the expanded region of the creative modifies the width and height of the iframe to take up the right area.

z-Index ensures that the creative is always visible on the top of the publisher’s page. This is largely useful for interstitial and other OTP formats where the creative is expected to show up over the page. You can learn more about z-Index from:
IAB z-index guidelines
w3schools z-index reference