Microsoft Teams is the new tool from Microsoft that combines chat, documents, people and tools in one place. It is the next evolution of Skype for Business.
To access it, just head to https://teams.microsoft.com where you will be proposed to download the desktop application. This is highly recommended if you want the best experience and be sure to not miss any message. Applications for Android and iOS are also available!
Please keep both Teams and Skype for Business applications running on your computer so you can communicate on both platforms for the time being.