One way to tackle the challenge of unfamiliar words is to use a dictionary. You could use a traditional printed dictionary, or an online dictionary, or both. A printed dictionary is easy to keep beside you wherever you happen to be reading. But an online dictionary holds the advantage when it comes looking up words quickly as you can look up a word in three or four online dictionaries simultaneously, to compare the definitions they offer.
You also have a choice between using a general dictionary, or a specialist dictionary for the subject that you are studying. How helpful you find either will depend on your subject, so it is worth doing a little exploring to find out. Note down a few ‘difficult’ words from one of your main textbooks. Then visit a bookshop, or go online and find a few dictionaries. Look your words up to see if they are included and whether the definitions make sense to you.
Dictionaries are an invaluable resource but don't expect them to be infallible. A general dictionary will often not include key words from your subject area, or will give a definition which is misleading because the nuances of meaning are not right for your subject. On the other hand, specialist dictionary definitions can be difficult to understand.