A matter of course means naturally/automatically/normally. When you do something as part of a normal procedure, without consciously thinking about whether you should do it or whether you want do it, it is a matter of course. Take a look at the following examples:
- A recent visit to France reminded me of the differences between the "new world" of America and the "old world" of Europe in approaching historic preservation. The French have been saving, restoring and adaptively reusing their architectural patrimony as a matter of course for many centuries. To us, 100-year-old buildings are antiques (Washington Post, November 19, 2010): Here, the author is emphasizing how old buildings are such a natural part of French cities by saying "a matter of course"
- By the end of the 1930s, most states in the world, including those that retained political freedoms, had imposed restrictions on trade, migration and investment as a matter of course. Some achieved near-total economic self-sufficiency (autarky), the ideal of a de-globalized society (from Niall Ferguson, The Ascent of Money): Here, the author is using "as a matter of course" to stress that protectionism was a norm across the world in the 1930s.
- Ortiz estimates that, just among the buildings his company represents, about 2,000 units in larger high-rise buildings have gone smoke-free. Add to those hundreds more in smaller buildings, down to two-flats and three-flats, not to mention individually owned condominiums whose owners have decided to rent them out as smokeless, he said (Chicago Tribune, November 19, 2010): Here, the author is emphasizing his point that a lot of buildings are going smoke-free by adding examples with "not to mention"
What you need to do, therefore, is:
- Use an English-English dictionary that gives you both the definition of a word and a few sample sentences from which you can learn the context to use the word.
- If your dictionary doesn't give you sample sentences, go to the websites of major newspapers (New York Times, Washington Post, Wall Street Journal etc.) and search the word. You will get hundreds of articles in which the word is used.