Slack is a web-based team communication tool that allows you to organize conversations and materials between multiple group participants. Three account types are available for a monthly or annual fee. Features for the Free account include:
Slack is accessible online. The Free version of Slack includes one-on-one voice calls, a maximum of 10,000 stored messages, a maximum of 10 third-party apps; and a maximum of 5 GB of storage.
Slack provides an online Help Center full of support articles on multiple Slack user topics such as Account Basics; Messages; Channels & Direct Messages; Notifications; Apps; Files; Tools & Communication; and Policies & Guidelines.
You can find additional Slack tutorial videos on YouTube.
Check out the Slack Help page, or submit your questions directly to Slack with the online Contact Us form.