The font that is the default to too small for me. Plus, when I cut and paste something from an email, even though I have tried changing the font to a different one, it doesn’t print out like the way I wanted it to look.
Hello,
adapt the font size in Tools -> Options -> LibreOffice Writer -> Basic Fonts (Western)
(Alternatively you may define a new default template)
Cut&Paste from email: If you want the Writer default fonts use Edit -> Paste Special -> Paste Unformatted Text
Hope that helps.
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Your question can be answered several ways.
###Reading the screen
You can have the printed material in default size (12 pt) and have the screen magnified. Look at the bottom right corner of the window, in the status bar: 
. Drag the slider to change the zoom factor. You can also click on the number and enter a precise value.
###Changing the default for the present document only
Display the side style pane with F11 or Styles>Manage Styles. Right-click on Default Style and Modify. In the Font tab, change the font face, weight or size.
###Changing the default for Writer
This will affect all past and future documents (provided there is no override in the document, of course).
Tools>Options, LibreOffice Writer>Basic Fonts (Western). Here you can set the default for various contexts.
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(edited only to remove misspellings)