Communication is very necessary isn't it?
To get in touch with users is easy and achievable in direct or indirect manners. Just write an e-mail to a single person or a group of users. This is possible at different points of the system like the users or group management, different course management functions or course elements like the E-mail module.
Notify participants of groups or courses by encouraging them to subscribe to course elements and they will find those news easily at the Subscriptions within their Home or by choosing to receive them by e-mail. For example a subscribable element is the Calendar, which can be used as a communication channel to foster a schedule.
If you want to connect to a logged-in user right away, there is the Chat which is easy to use at any point of the OLAT LMS.