VSTS is a service company typically prefer using, as it's more private, and lacks the community-style approach to sharing and publishing your code. VSTS builds upon the older TFS style, but at the same time, it's a modern and fresh take on performing the whole ALM process and Agile project management tooling within a single service.
You can provision a new VSTS account at https://www.visualstudio.com/. The basic service is free for up to five users, which typically is sufficient for smaller SharePoint Framework projects.
If you own a Visual Studio subscription, you can also access the basic services of VSTS.
VSTS has an amazing selection of tools and services, which can be easily configured to support your ALM process, big or tiny.
Initially, you can just use VSTS as a place to store your code and not worry about much else. Later, when your project grows larger, you can involve additional aspects of VSTS, such as automated testing, user load testing...