How do I set my siteURL instead of having http://localhost:8888/? I downloaded and installed Craft Personal on my computer and choose /websitetest/ as my website name. I used MAMP and phpMyAdmin to create a database.



Still to access my website the url is http://localhost:8888/ and when I try to access http://localhost/websitetest/ I get the following error message: Forbidden
You don't have permission to access /websitetest/ on this server.



Moreover in my index.html file, when I call for an URL entry:

href="{{ entry.url }}"

by default it redirects towards /websitetest/_entry , which displays me the same error message, while localhost:8888/_entry works when I test it manually!



Some ideas where can this come from?

Thanks!
Unless instructed otherwise, MAMP uses port 8888. You can tell it to use the "default" ports, which will mean the site gets served over port 80, and your URLs no longer contain :8888.

As for the other issue, it sounds like you haven't set up your site's document root correctly. Either way, it's a MAMP configuration issue, not a Craft issue.