In the module's xml file add a section for parameters.

<params></params>

Input

<param name="sample_input" type="input" default="default value" 
label="Sample Input" description="Mouseover popup description." />

Radio

<param name="sample_radio" type="radio" default="1" label="Sample 
Radio Button" description="Mouseover popup description.">
<option value="1">Yes</option>
<option value="0">No</option>
</param>

Textarea

<param name="sample_textarea" type="textarea" default="Pre-populated 
sample text." label="Content"rows="30" cols="4" description="Mouseover 
popup description." />

Select

<param name="sample_select" type="select" default="" label="Sample 
Select List" description="Mouseover popup description">
<option value="">Select One</option>
<option value="1">One</option>
<option value="2">Two</option>
<option value="3">Three</option>
</param>

The values are retrieved as follows:

  $input_value = $params->get( 'sample_input' );

  $radio_value = $params->get( 'sample_radio' );

  $textarea_value = $params->get( 'sample_textarea' );

  $select_value = $params->get( 'sample_select' );