Although both Git and TFVC are source code systems available in Azure DevOps, they are very different to work with. 

As I mentioned, the default source code system is Git, and you should be able to use that for almost all of your projects. If you'd like to learn about the differences between Git and TFVC, then you should check out the article on Microsoft Docs at https://docs.microsoft.com/en-us/azure/devops/repos/tfvc/comparison-git-tfvc?view=azure-devops.

If you are currently working within a TFVC repository, then don't fret—there is a way to move to Git if that's what you want to do. There happens to be a tool with which you can migrate from TFVC to Git, and you can read about it and download it from: https://github.com/git-tfs/git-tfs/blob/master/doc/usecases/migrate_tfs_to_git.md.