Is the software already installed in mac os ? I'm running mountain lion.
You need a text editor and some graphics software for designing icons etc.
Google "install apache mountain lion" for details on how to get the built-in Apache web server running. However, its probably easier and quicker to install MAMP (
http://www.mamp.info/en/index.html).
Text-editor-wise, the built-in TextEdit isn't really suitable. For the basics, you can't go far wrong with TextWrangler (free from the App Store). If you want more bells-and-whistles (such as automatic completion/templates/online help for HTML, CSS and Javascript, preview/debugging) others in this thread have already suggested apps like Coda and Espresso - which mostly cost money. If you want something along these lines for nothing check out
https://netbeans.org.
Graphics wise - you don't have to run out and spend an arm and a leg on full Photoshop. Photoshop Elements will do nicely at a fraction of the cost, or Pixelmator (App Store - relatively inexpensive) will do the job for drawing icons. Pixelmator is far better-looking but I'd rate 'PS Elements' much more capable when it comes to format conversion, cropping, resampling etc.
Personally, though I much prefer a vector graphics package for icons & backgrounds - I use Xara Designer - which is absolutely brilliant apart from the minor problem that it is PC only & I run it under Parallels - yet to find anything comparable for OS X.
I've heard of python and a few others but what's the most user friendly to start with ? But I'm also not looking to make a website that looks too childish..
As noted by others, start with HTML and CSS - that's all you need for 'static' webpages.
Programming languages like Python run on the web server and generate custom pages - in particular, pages created with 'live' information from a database rather than from static html files, and... I'm going to annoy a lot of Python fans here... the language of choice for this is usually PHP. PHP is a horrible fugly programming language, but it was designed specifically for dynamic websites and comes with a huge library of really useful functions. More importantly - if you want to create a website that can be uploaded to commercial web hosting services - PHP is by far the most widely supported server-side language.
Data for dynamic websites is managed by a database on the server, and the situation here is similar: there are better databases than MySQL, but MySQL is the one supported by most web hosting services.
PHP and MySQL are included in the MAMP application.
As mentioned in another thread - if you want to create a dynamic site that can be edited and maintained by other people then, these days, it is more sensible to look at a Content Management System like Drupal, Joomla, Wordpress (and many others) than to try and roll your own in PHP. You'll still need HTML and CSS skills, though, if you want to customise the templates to make your site distinctive.
Increasingly important is Javascript - another programming language but this runs in the user's web browser and is used to improve interactivity, add animation etc. (anything from checking data on a web form before sending it to the server, to writing full-blown office apps and games). Safari, Firefox and Chrome have built-in javascript debugging).