In 2016, Salesforce acquired a company known as Demandware, and re-branded their solution as Salesforce Commerce Cloud. Later, in 2018, Salesforce acquired a company known as CloudCraze, and that later became known as Salesforce B2B Commerce, and the original Demandware acquisition became known as B2C Commerce. One key difference between these two solutions is that the B2B Commerce product runs “on platform”, and the B2C (Demandware) product does not.
The development paradigm for B2C Commerce Cloud relies on developer knowledge of server-side Javascript (similar to NodeJS, but is actually Rhino Javascript). Similar to the Marketing Cloud (ExactTarget) product, developers who are used to developing with Salesforce DX, Lightning Web Components, and Apex will find that there is none of that here. The entire solution is different, however that has changed somewhat with the introduction of add-on products like Salesforce OMS, Salesforce Loyalty, and other features which run on-platform, but are integrated with B2C Commerce. Additionally, there is in-fact, an accelerator from Mulesoft, which will let you quickly connect your B2C Commerce instance to your core sales/service instance(s). It is not required to integrate the two, but does greatly simplify the process.