[SalesForce] How to get this button to pass data to controller

UPDATE

I have the following function:

<apex:actionFunction action="{!selectRec}" name="recordSelectFunction">
                        <apex:param name="selectedID" assignto="{!selectedRec}" value=""/>
                    </apex:actionFunction>
        </apex:form>

And this, inside of an iterative block (where the iterated var record is "item".

<a style="cursor:pointer; font-size:14px" onclick="recordSelectFunction('{!item.Id}')">Select Record</a>

Based on documentation, expecting onclick to call that apex:actionFunction, which passes "item.id" as the parameter, meaning my controller var would be set to that ID. !selectRec in the controller simply prints out the variable to start, and it's null.

I would like a button to be clicked and use param to set a certain variable in the controller to a value from the VF page. I am hoping someone can either tell me why it's not possible, or (hopefully) how to correctly develop this. See bottom for link to the StackExchange question that got me started.

I have a block table that loops over a list of records from the controller, and I output things like a date field, ID, Name, etc. and the last thing I do it add the following button:

<apex:form>
 <apex:commandButton value="Select Record" action="{!selectRecord}">
                         <apex:param name="recordID" assignto="{!selectedRec}" value="{!item.ID}"/>

                         // "item" is the iterated var

  </apex:commandButton>
  </apex:form>

the goal is for that button to call a function

public pageReference selectRecord(){
    system.debug('the record ID is : ' + selectedRec);
    return null;
}