Userplace openform is the pluign which provide the frontend submission facility in the theme. This plugin is a extension of Userplace plugin. If you have already checked the Userplace plugin docs and videos. Then you should understand easily the next section. If you haven't configured Userplace first, either won't understand this plugins functionality.
If you haven't installed all the pluign during theme installation then please install all of the plugin before you go any further.
If you are a logged in user then you should get an Add Listing button in the top right cornet of the page. Click that button. You will be redirected to a page like below
In this add listing page your user will be able to add listing from frontend. You can check there are bunch of form there to add the listing.
You can check in the sidebar there is another menu All Listing which shows all the listings of the current user. Check below image
