PHP/phtml files
You can use this to check your enabled/disabled settings:
Mage::getStoreConfigFlag('path/to/enable_disable') // returns true or false
For all other config values you can use:
Mage::getStoreConfig('path/to/configfield') // returns config value
Layout files
In layout.xml files you can check boolean config values like this:
<reference name="head">
<action method="append" ifconfig="path/to/enable_disable">
<block>my_block</block>
</action>
</reference>
If you want to use show something based on you config string values, you may need an helper method:
<reference name="head">
<action method="append">
<block_id helper="yourmodule/yourhelper/checkConfig"/>
</action>
</reference>
Your_Module_Helper_Data.php
public function checkConfig()
{
$config = Mage::getStoreConfig('path/to/configfield');
// your logic here
}