To use the advanced settings on posts firstly you must create one, the guide to do this can be found here.
While creating your post you will see a settings icon appear at the bottom left of the text box.
Clicking this icon will expose the advanced settings.
Clicking the selector next to 'show as a sponsored post' will highlight a sponsorship deal to your members via messaging in app.
Clicking the drop down to the left of 'pin at top of the feed for' will expose the duration of time you can pin a post for.
Pinning a post ensures that content stays at the top of either the 'official' or 'community' walls for the period specified.
When you're happy just click post!