Text Edit is the built-in word processor that comes with your Mac and it is the easiest way for new users to produce letters, documents, etc. Most of it is self explanatory. Most of what you need (fonts, font sizes, colors, etc.) can be found right across the top of your window. Here are some tricks that can help you be more efficient.
You can select several non-adjacent bits of text simultaneously and modify them all at once. For instance. I could change the heading style for all the subjects in the document. To do this, highlight the first bit of text and then hold down the Apple key as you continue to highlight and additional text. Once you have all your text selected, you can change it.
Using this same method, you can also drag any one of the highlighted portions to a new area, confident that the other chunks will come along for the ride. All the selected areas wind up consolidated in their new location. If you want to copy the text to the new area rather than cut it, hold down the option key while you move it.
The Apple key + the T key will open the standard Font panel.
The Apple key + the F key will open Fine. With that you can find all instances of a certain word in your document and change it if you wish.