1. look up the words you don't know
2. re-read the article and replace the word you didn't know with the definition of that word
3. If you still don't understand, discuss it with another fellow classmate or what I do is try to find information about the article such as when was it written and who is the audience. Knowing when the article was written helps the reader understand the context of the article and will clear up some confusion.
4. If after finding info about the article and you still don't understand it, email your teacher, inform him/her what you have done to try to understand it as well as tell them what you think the article is about, and ask them if you are thinking in the right direction. If they see that you have put some effort, then they will be willing to help you out.
Hopefully this helped and good luck.