You need to include a checkbox field on each row by making use of Wrapper class that wraps each and every record with a selectable checkbox. Please follow the guidelines explained in the below article
here i don't use any check box or radio button,just by click on rows only i have to select multiple <apex:page standardController="account" recordSetVar="arecs"> <apex:pageBlock >
http://wiki.developerforce.com/page/Wrapper_Class
<apex:page standardController="account" recordSetVar="arecs">
<apex:pageBlock >
<apex:pageBlockSection title="Account Records">
<apex:pageBlockTable value="{!arecs}" var="item">
<apex:column value="{!item.id}"/>
<apex:column value="{!item.name}"/>
<apex:column value="{!item.phone}"/>
<apex:column value="{!item.billingcity}"/>
</apex:pageBlockTable>
</apex:pageBlockSection>
</apex:pageBlock>
</apex:page>
sample to practies guide me urgent
http://salesforce.stackexchange.com/questions/23333/get-data-when-click-on-row-in-pageblocktable