This depends on your subscription, when it was signed, and the size of your tenant. Her are the basics: Skype for Business Online will be retired on July 31, 2021. From October 1, 2018, this is the rule:
New Office 365 tenants with 500 or fewer licensed seats will have to use Teams. These tenants won’t have the option to use Skype for Business Online. Then again, you have to ask the question whether they want or need to use Skype for Business Online? Existing tenants aren’t affected by the news.
Teams is a better option.