Here are a few of the tools I recommend:
Your email list (the "glue" of your online business)
I really like ConvertKit. Solid product and it's backed by a great team.
If you're a "creator", not only will CK give you everything you need but the product is positioned toward people like you (i.e. you sell stuff online – most likely immaterial/digital products – then you're who I'm talking about.)
Lots of great automation functionality, Liquid templating (for easy personalization), and more.
I'll get around to writing a proper review soon, but I have a hefty course on how to strategically use ConvertKit.
Here's my affiliate link (thanks for the support!)
Your website (where you'll build your audience + refer people to)
I've historically used WordPress, but I'm currently using Statamic because it fits what I'm looking for in a content management system – namely, something geared toward more technical people that's extremely well-built and designed and flexible.
If you're not technical, don't use Statamic. Use WordPress, Squarespace, or something that's both hosted (i.e. runs your website) and includes a content management system and a healthy ecosystem of themes.
How you sell (what keeps the lights on)
There are a number of ways you can sell your products/services, and it largely depends on