No, there is no automatic way to import content from static html files. You would have to re-create those pages in mojoportal and you could copy and paste content from the existing pages. I would use the Paste as Text toolbar item in the editor to remove all html m,arkup from the pasted content and then reformat it using the editor.
You should watch some of the training videos from here to get up to speed on using mojoPortal first:
There is also a Html include module in mojoPortal that may be useful for you. You can add an instance of this module to a mojoPortal page and then point the module at an html file. The files must be located in a specific folder /Data/Sites/[SiteID]/htmlfragments
Note that you would need to modify the html files to remove the outer html tags, ie remove html, head, and body tags and leave only the content that was inside the body tag. Hence the name Html fragment. mojoPortal already provides the html, head, and body tags and they are not allowed to be duplicated, so your html fragment files can't have those tags in them.
There is also no easy answer I can give you about integrating your existing ASPX pages, you will need to get up to speed with the developer documentation in order to come up with yur own integration strategy.
Hope it helps,