How to best test Conversion & User Journeys?

Hi all!
I work for a social media startup with a product that could be summarised as a gamified version of Instagram. The MVP has been live for only a couple of months so we are still trying to validate the product purpose in line with user needs.

At this point I need some advice on what tools to use and how to set up a structure to test the customer journeys from digital ads( on fb, twitter, instagram) to our landing page and somehow convert this into a conversion strategy. Could even be static mockups as long as we get actual feedback from users into what would make them register to our website.

Any discussion or ideas would be veeeery appreciated!

Thank you all