Microsoft provides Teams on a range of different pricing plans, depending on both your needs and usage. If you're just after actual video calling through Microsoft, it'll shift you straight to Skype, for a start, but that's not a package that supports the kinds of collaborative features most business users will want or desire.
You can access Microsoft Teams for free with just a Microsoft account. So if you've got an Outlook email address (or kept up an old-school Hotmail one from back in the day) then you can sign in to and set up Microsoft Teams that way. However, that's an option that's only available if you don't have an Office 365 subscription tied to that email account. That's because Teams was and is part of the business suite of Office 365, with tiered pricing depending on your needs.
At the free tier you can have up to 300 users in your organisation, but they'll have to live with just 10GB of shared storage between them. While you can manage video group calls, there's no facility to record them for later training or review purposes. The free tier also lacks administrative tools for managing your users and their application use, as well as usage reporting for Office 365 services.
If you do want or need the more complex side of Microsoft Teams, you'll need a business or education licence for Office 365 in place. Microsoft does provide consumer-level Office 365 subscriptions, but Teams is explicitly not part of the Office 365 package in the consumer space. Again, Microsoft probably figures you'd be happy enough with Skype's simpler video and voice tools.

Because it's part of the business version of Microsoft Office 365, there really isn't distinct pricing for just Microsoft Teams. Office 365 Business Essentials, the cheapest business tier of Office 365 that includes Teams runs at $6.90 per month per user with an annual commitment, while Business Premium will set you back $17.20 per user per month. Finally, the enterprise-grade version of Office 365, Office 365 E3 costs $29 per user per month. That tier is the only one that punches the number of individuals up from 300 on the Essentials or Premium tier. Although it does so quite a lot, because it supports an unlimited number of users.
Microsoft provides Team apps for all major desktop operating systems, as well as mobile and tablet devices and via straight web delivery in situations where you don't want to or can't install software. However it doesn't fully support every browser when trying to use the web interface; predictably Edge and Chrome are fine, but Apple's Safari browser, for example isn't fully supported. You may have to heavily tweak cookie and tracking features in more privacy-conscious browsers such as Brave.
The core Teams interface will be immediately familiar to anyone who's used tools such as Slack, with a left side column for each Team you create. The UI is quite good in this initial set-up process in terms of guiding you through creating private and public teams, although it may take some time to wrap your head around the way that Microsoft compartmentalises just about everything in Teams. You might think that a Team would be like a Slack channel and you'd start chatting there, but instead they're containers for actual channels that sit under this kind of hierarchical structure.
Likewise, each channel within a group can host not only chat but separate default tabs for file sharing and wiki creation. Those are just the defaults. It's entirely feasible to integrate every single Microsoft Office app and a huge variety of third-party productivity platforms including CRM, training, development, calendars and much more as their own tabs.
It's a very powerful approach to providing every possible need, but like Microsoft's Office apps, it also means that you may have to click or tap around quite a lot in order to get to precisely where you need to be.
Much of that depends to an extent on how you set up Microsoft Teams and quite how many teams, channels, chats tabs and individuals you have to manage. Microsoft's clearly gunning for Slack and its ilk with Teams and the clean Office-like interface here is a plus in familiarity terms, but also a bit of a minus if you're more used to Slack's streamlined chat-centric approach.