Being new to SharePoint, I will give you some higher level troubleshooting tips to get you started. First check IIS. All of the sites except the default site should be started. If it is started, right click, manage site, browse. This will try to open the site on the server. Does it open? If so the issue is most likely between your workstation and the server. If not what is the error? This is crucial because you troubleshoot different errors in different ways. As another general tip, especially with SharePoint. When requesting assistance, please provide as much detail as possible. Describe what you see on the screen and any specific error messages on the screen. Saying the site is not accessible could mean 500 different things to different people.
If it is a SharePoint error, is there a Correlation ID? If there is, run the following command:
merge-splogfile -Path c:\merged.log -Correlation <INSERT CORRELATION HERE>
This should create a log file that merges the log entries from all the servers in your farm from the last hour into one file and only includes errors related to the page request that caused the error. Make sure the correlation you are searching for was generated in the last hour. The correlation changes on every page request. If you need to go back further than an hour, use the -StartTime switch. More information can be found here:
Now look through the log and find anything that looks like a possible cause for the error. If it isn't clear straight away, post the log here after cleaning it of any corporate secret sauce.
Hopefully this will get you pointed in the right direction, and if not it should at least get you more information to post back here.