When you installed QuotePress a new sidebar menu for QuotePress was created. Select "Add New" from the menu and fill out the form:
Note: when setting the feature image you must click "set feature image" on the media manager interface.
After you setup the quote, press "publish" to save the quote and make it available to your pages, posts, widgets, and mobile apps.
Go to your page or post where you want to show a quote. Enter the [quotepress] shortcode.
Without any extra parameters, this will display a list of quotes based on the defaults set on the settings page.
So, to display a list of quotes you would enter:
[quotepress]
To display a specific quote you'll need to specify either the quote ID or the shorthand:
[quotepress id="14"]
or
[quotepress shorthand="some-name"]
For more information, visit the QuotePress wiki.