Ukrainian is one of Slavonic languages (others include Polish, Russian, Bulgarian, Czech, etc.). It shares quite a few things with its closest neighbors, Belorussian, Russian, and Polish, but it also has its own unique grammar rules, vocabulary, and usage.
As any other language, Ukrainian has its varieties and dialects that are spoken in different parts of the country. A most commonly recognized distinction is between the language of Western Ukraine (roughly west bank of the Dnipro river), which is a bit closer to Polish, and that of Eastern Ukraine (roughly east bank of the Dnipro) more influenced by Russian. Eastern Ukraine and southern peninsula Crimea also have a large percent of the Russian speaking population. Please note that the "linguistic" geographic line between the "East" and the "West" is much finer. These language differences have very deep historical roots. This paragraph should give you a general idea about Ukrainian language variations.
Another important difference is between "popular Ukrainian" and "standard Ukrainian." Language influences have played their roles here, too, but for our purposes it is important to know that "popular Ukrainian" significantly deviates from the standard norms described in grammar books and dictionaries and may in fact be a mixture of Russian and Ukrainian, or diluted with a good many Polish words. This is of course a natural process found in any language. "Standard Ukrainian," which is taught in this course, does not exclude colloquial forms, but generally adheres to language norms. In other words, you won't be taught belles lettres Ukrainian, which would sound irrelevantly fine in everyday speech. You will find here lessons of "educated speech" that will be universally understood in Ukraine. The author of this course lives in Kyiv (the capital of Ukraine) and will try to teach you standard Ukrainian as defined by her environment and, of course, Ukrainian language rules.
Major differences of the Ukrainian language from English include:
Special grammar lessons that you'll take upon mastering some simple vocabulary will familiarize you with most of these differences. You will learn some basic rules for nouns, verbs, and sentence structure, as well as new vocabulary.
So, off we go. Enjoy and good luck!