Old English hit, neuter nominative and accusative of third person singular pronoun, from Proto-Germanic demonstrative base *khi- (source also of Old Frisian hit, Dutch het, Gothic hita "it"), from PIE *ko- "this" (see he).
The word the is very important to native speakers of English because it is used to divide the world we process through language into two categories: old information and new information. It helps us to divide the world into things which we agree are known, or important, and things which we feel aren't.
Here's another way to explain it: The is used to refer to a specific or particular member of a group. For example, "I just saw the most popular movie of the year." There are many movies, but only one particular movie is the most popular. Therefore, we use the.
There was no first word. At various times in the 5th century, the Angles, Saxons, Jutes and other northern Europeans show up in what is now England. They're speaking various North Sea Germanic dialects that might or might not have been mutually understandable.