There are a number of options to pick from for building a website. There are two types. One type is a combination of a hosting account and interface to build a website. The other type is software you install at a website hosting company.
The first type for building a website is something called a website builder. This is a company that will host your website and proved an interface to build the website too. Two examples are Wix and Squarespace. Both allow you to build a website with different features depending on the pricing plan you select. There are two big negatives for building niche websites. The first is flexibility since you are limited to the features they provide. The second is you are bond by their terms of service so you need to confirm your monetization model will work.
The second type is installing your own website software. There are a number of choices including WordPress, Drupal and Joomla. These are open-source projects which means they are developed by a community and available for free. Each has their pros and cons. I would recommend WordPress because it is very popular and you can find a lot of information on the Internet about how to configure it for niche websites.