Fonts Help

[Djones9976]

I have been reading with interest the discussions about fonts, which has always been a problem for me.  Presently, I am using TexShop version 4.44 with the font setting at Arial 18 and encoding at unicode UTF-8.   When I try to change the font in a section of my work, every command I put in is ignored, completely ignored.  How am I supposed to change fonts?
Thank you,
D. W. Jones
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