How do I...
a) send an e-mail to students through Canvas
b) how to my students register to receive notifications so that they remember to join in discussions...
HI @withjude888 you could use the Inbox facility in Canvas to message your students.
However, you may need to remind them to ensure their Inbox notifications are set correctly with these guides:
The last two guides will also help students to set notifications correctly for discussions. You might need to suggest how you would like them to set these up.
Sing out if you need a hand.