Follow the given steps to create a chat room for your Students:
Login to your Teacher Account
Click on "Chat Rooms" tab on the Home page
On the left column in the Chat Room, click on (+New) sign and "Create Channel" to create a new channel
Type in the name of the new channel
Add a short description of the channel
Add your students to your channel (You can also make a private channel)
Click on "Create Channel".
After your channel is created successfully, type in the message and send it to your students.