For Example if I start my announcement with hello …. Instead of students is there a function I can put in where it will Say hello Leanne?
I don't believe there is a way to do this. Also, I wouldn't recommend it. Unless you also assign the announcement to each individual student, all of those announcements would be visible to everyone in the course. Announcements are designed to sent out to groups of students.
For individual communication I would use the Inbox. Unfortunately, I don't know of a way to do what you desire using the Inbox, either. You could create the content of your message in a word processor and use mail merge to create individual messages, then copy paste them to each individual student's email.
There are some third party tools that work with email that allow you to do this. For example, https://emailanalytics.com/mail-merge-gmail/#:~:text=Mail%20merging%20in%20Gmail%20is%20a%20strategy....