Most foreign language textbooks include so much material that you would need to have class every day for a year and do massive amounts of homework every night in order to cover everything. Then there’s the workbook and the accompanying online exercises…even if you love the language you are studying, that’s overkill. All of these exercises and activities make it easy for an instructor to create lesson plans that match the interests and abilities of the students. Plus, instructors don’t want to be bored, either.
Most students only do what is assigned and ignore the rest of their book–but that’s a waste! At exam time (chapter exam or final exam), all of that extra material makes a good review.
Some instructors even take exam questions from the textbook or related materials. I’m just sayin’…
So, you are studying your vocabulary diligently, including the el or il or le or der in front of some of the words. Many vocabulary lists that you find in textbooks include the definite article (the ‘the’). You may think that native speakers always include the ‘the’, but the real reason textbook publishers include the ‘the’ is to give you a heads up about the gender of nouns. English speakers sometimes have trouble associating gender with nouns. Some English nouns are masculine or feminine if they refer to people or animals (waiter or waitress, rooster or hen). Other nouns like book or car or phone just do not have gender in English. While there are rules to help you remember a noun’s gender, they can be hard to learn, hence the helpful hints.
That does not mean that you need to include the definite article with every noun. You might need an indefinite article (an ‘a’), or no article at all. I had a student who kept referring to THE Wendy. Another student said that she was THE woman.
Those definite articles are definitely handy, but look at examples or ask your instructor if you are not certain when to use them in a sentence.