I want to publish it with a third-party domain that I've already paid for, how can I do that?! should I go to file => export => then export it as an html file, then go to a software as "espresso" and publish it through that?
Yes, you're on the right track. Design your site and when you're ready to go live, go to File -> Export as HTML. You then have your HTML, CSS, Image folder and everything else saved to your HD together.
I have not heard of "Espresso" I looked at the link you provided and it seems to be an editor of some kind? You don't need to edit anything else or run it through software like that. Might be making it too complicated. Personally, I would download Mozilla's free FTP ( File Trasfer Protocol ) software "Filezilla". You use Filezilla to transfer your HTML, CSS, Image files etc. to your 3rd party server and volia! Done. Super easy and painless. All you need to get your files up to your 3rd party server is a simple FTP, nothing else.
http://filezilla-project.org/
The second question is: assuming I had published the site via "espresso". After a few weeks I want to change stuff in my website (add a picture, text etc)
As mentioned already, you don't need to use Espresso at all.
If after a few weeks you want to change something on your site, you go back to your orginal Muse file ( i.e. yourwebsite.mu ) like you would open up an previously used InDesign or Illustrator file and adjust your design. Add things, remove things, whatever you want. After your have made your edits, re-save and then repeat the process as before. File-> Export as HTML. Collect your files together again and use Filezilla to re-upload your site. I have personally found that Muse created sites work better if you re-load the whole thing again. That way you don't accidentally exclude something the site needed. If you know what you're doing and know what would have been affected by your edits, I have just uploaded the changed page's HTML and the corrosponding CSS and imahge files. But the foolproof way is just to re-load the whole thing.
It's very easy, painless and you don't need any other bit of software like Espresso unless you're intending to do something that you haven't explained in your post. I hope that helps.
