Can PowerApp develop both web parts/apps for both SP2013 web sites(online or on prem) and for mobile platform?

Hi,

Reading this article here, https://powerapps.microsoft.com/en-us/blog/powerapps-and-sharepoint/

It seems to be describing the PowerApp can develop apps for both Web and Mobile.  Our SharePoint Administrator is saying that PowerApp is only for developing Mobile app.  Can someone please clarify for us?  Thank  you

Also, will apps developed with PowerApp will address the current performance problem?   A couple of our SP web site pages are loading up the web parts/app parts very slowly.  It displays "Working on it....." for a good 5-10 secords.

Thank you.

Thank you