I have been trying to change styles for hours. How does one do it?

[Wim1]

I am on Mac El Capitan.
I have recently changes from AA open office to libre OO.
I am using word. Their default style is maybe good when one uses a microscope. I like to change both font and size and find it impossible to do. Anybody can give simple instructions? I’ll be very grateful

[charlie.it]

Hi, can I help you with a screenshot ?

P.S. In LO and OO you are using Writer, not Word!