edit the permission levels on your site. The way to do that is to first go to the edit permissions page for your site located at http://my_web_site/_layouts/user.aspx. Click on "Settings" and you should see:

Click on "Permission Levels" and then click on the level that you want to grant personal permission access to. You should see a long list of available permissions that can be granted to that particular permission level. At the bottom, you should see:

These permissions grant the user the ability to create personal views of web pages. They are pretty self-explanatory.  Afterwards, the user will now have access to a new item in their personal menu:

Once the page is personalized, two new items will appear allowing the user to view the shared view and the ability to reset their view back to the shared view.

Personal customizations are one thing that makes portals useful. I hope this post helps.