@Phillip you need to concatenate the field call with the rest of the URL you are creating. <a href="
https://system.netsuite.com/app/accounting/transactions/purchord.nl?id="||{createdfrom.internalid}> Purchase Order link</a>
if that URL does not work, it is because the quotations are not quite right.. if you suiteanswer it there are a bunch of URL creation examples you can steal from.