Let's clean up some terms...
Ubuntu is a distribution ("flavor") of an operating system based around the linux kernel. It is not a server.
Apache is a project name (foundation name too) for a web server software product. Apache's actual program name when executed is traditionally 'httpd'.
There are other web servers out there, so use a little care in requesting "apache" and "httpd" vs. "web server".
As to installing Apache, normally distributions - Ubuntu inclusive?! (I don't use it) - have a packaged installation for apache/httpd. When you install apache you will more than likely want to install a number of other components such as modules and language parsers (i.e. mod_rewrite, mod_vhost, php, mod_perl, mod_ssl, xml support, mysql support, etc.)
Installing a typical linux-based apache installation normally is refered to as installing a L.A.M.P. configuration. LAMP= linux apache mysql php/perl/python.
It sounds to me that you have a need for some serious foundational reading in order to get yourself rolling. Typically forums like this don't provide the kind of foundations-building narrative you might need. I recommend the following reading lists:
The Apache forum FAQ here on tek-tips:
Wikipedia on LAMP
Some googled results on installing LAMP on Ubuntu:
An especially nice forum dedicated to Ubuntu:
Good luck!
D.E.R. Management - IT Project Management Consulting