We use instapage for building our landing pages and we are new to Marketo...so I'm having a bit of trouble getting my head around some things.
I already integrated instapage and marketo.
But now, when I click -in instapage- "publish" it asks for a unique URL for the landing page. Can I create a URL in Marketo without linking it to a LP template within marketo?
Off the bat, I have to tell you that InstaPage's integration is dangerous and ill-thought-out. It represents a denial of service (DoS) vulnerabilty against all your Marketo integrations, since they haven't taken into account REST API call limits. A hacker can easily disable integration access to your Marketo instance using their InstaPage connector.
Naturally, this is not good, and I wouldn't use this integration in a professional environment. Rather, you can (and should) use the Marketo Forms 2.0 API to submit InstaPage form data to Marketo. This is the secure and scalable way to integrate.
At any rate, the answer to your question is that Marketo-hosted URLs that aren't tied to Marketo-hosted LPs -- that is, Redirect Rules in the Marketo Admin UI, since that's the only place you can do such a thing -- can only redirect people to a separate InstaPage (sub)domain.
That is, you can have pages.example.com/marketo-lp.html as a Marketo LP, and pages.example.com/instapage-lp.html redirect people to instapage.example.com/instapage-lp.html. But you can't have pages.example.com transparently show InstaPage LPs without the URL visibly changing for the end user, since once you dedicate pages.example.com to Marketo, it can't simultaneously be a CNAME for your InstaPage pages.*
* OK, technically with a reverse proxy you could share the domain, but I doubt you are technically prepared to do that.
Well, using the IP page builder is fine (and they sure look pretty) but as with similar services -- Unbounce is another -- the built-in integration should not be used. You should instead get a front-end developer to use the Marketo Forms API. The page still looks the same, but there is complex stuff going on under the hood to make it work at scale + safely.
As far as sharing a single subdomain between InstaPage and Marketo, that's not an easy hurdle. As I said above, if you have technical staff capable of managing a reverse proxy or CDN setup, then you could have pages.ejemplo.com/marketopage.html hosted on Marketo while pages.ejemplo.com/ip/instapage.html is published to InstaPage (note the extra "/ip/" in the latter path). You do that by adding the path in the InstaPage Publish dialog:
But again this requires technical configuration so pages.ejemplo.com can be shared. It's the kind of crazy thing I like to do -- but I understand suggesting it to others can be unreasonable.