A: The Portal Management app lets you do advanced configuration actions on your portal.
Open the Portal Management app.
Go to Portals > Web Pages.
To edit an existing web page, select the web page name.
Enter appropriate values in the fields.
Select Save & Close.
D: To use the WYSIWYG editor:
Edit the portal to open it in Power Apps portals Studio.
Select the page on which you want to add the component.
Select an editable element on the canvas.
Reference:
https://docs.microsoft.com/en-us/powerapps/maker/portals/configure/web-page
https://docs.microsoft.com/en-us/powerapps/maker/portals/compose-page
https://docs.microsoft.com/en-us/powerapps/maker/portals/compose-page