HOW DO I TYPE A LETTER ON THE MACBOOK PRO?

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There are some apps you can use to do it:

1. Microsoft Word. Word is available for OS X, and you can use it if you are familiar with Microsoft Word > http://www.microsoft.com/mac

2. Pages. It's Apple's Word version and can be get in the App Store. If you need basic features, it will work correctly.

3. LibreOffice. It's free, so you may want to try it first before the other applications > http://www.libreoffice.org

As mende mentioned, LibreOffice is very "Word" like, but more user friendly, and it's free. Download it, and try it out. It will seem like Word, only better.

For simple typing tasks you could use TextEdit. For more advance word processing needs, you could use Apple's Pages (available at the Mac App Store)