Screen keeps jumping around / expanding so I cannot send emails.

Trying to use my new Inspiron 15 and when I am writing emails and looking at things it just keeps expanding the screen whenever it likes.  I have looked at this seems to have been to the case since at least 2018.  Can anyone help me in very simple layman terms? 

I just cannot reduce them back so I cannot send a message because the Send Button is no longer visible - it is making work extremely hard and I think I will have to go back to my old laptop.

Thanks