Hello there, @mkocakulah ...
@Bobby2 has given you some excellent resource which should help to answer your question. Thanks Bobby! I wanted to quickly chime in just to mention that technically speaking, Canvas does not have "e-mail". I posted a response to someone early last year which still applies today...so you might want to read through it: Sending email to students. I hope this extra bit of information will be of help to you, Mehmet.
I'm going to add one more comment as well. Depending on your use case it might be better to post a course announcement instead of using the InBox. In both cases a notification will go out to all of the students in your class based on their notification preferences. But with an Announcement it is also in your course site in Canvas for them to find later rather than digging through the InBox. I try to post anything related to a course in the actual course whenever possible. I normally reserve my use of the InBox for sending messages to individual or groups of students.