A basic question, just want to type a letter on plain paper to print, how do I do that?

Are you asking how to print a hard copy of a letter you composed using Pages? If so then hold down the Command key and press P. Then a print dialog will open, select the printer you want to use, and click Print. Of course you must have a printer connected your computer. You can also place a Print command in the toolbar for easy access in the future. From the View menu select "customize toolbar", click and drag the Print icon to place it on the toolbar anywhere you like

If you have Pages then that will do for writing letters, open Pages and select New Document and then a dialogue should pop up offering different templates, just select Blank or select Letters and choose a format from there. There is also Text Edit in your Applications folder which is a very simple text editor.