Setting Query String Parameters in Links
You can set query string parameters in links to pages by constructing the link URL manually, or by using <apex:param> tags within the <apex:outputLink> tag. For example, both of the following examples create identical links to an external page:
The latter method, which uses <apex:param> tags instead of manually creating the URL, is preferable for stylistic reasons.
In addition to <apex:outputLink>, use <apex:param> to set request parameters for <apex:commandLink>, and <apex:actionFunction>.