ordinary - nothing special (ordinary beer, ordinary house); normal - within the expected range for a population -( normal height, normal sized nose), and usual - most frequent ("my usual" could be said in a pub if you want your usual drink from the barman, or i usually have fish and chips). These 3 words could often be used for each other general - many uses - general purpose sandpaper (sandpaper with many uses); "the general rule " - what tends to happen but sometimes not. "in generaI" is very similar to usually. overall - said when you are summing up "overall it was a good year" "overall he is an excellent footballer"

There are quite a lot of words there and many mean different things depending on how they are used. I may be easier to learn what to use when via practice and get a feel for when to use one or the other. Two words that can be used in the same way to mean the same thing are called 'Synonyms' and you can use a 'Thesaurus' to look up alternatives to these words (you can also find opposites or 'Antonyms' in thesaurus's, http://www.thesaurus.com/ is useful for this). Synonyms and antonyms are only correct for that given meaning of the word though, and some of those words have many meaning depending on use; ('General' according to dictionary.com has 12 different meanings!) Sorry I cannot give you something easier to explain everything, maybe someone else can but English is a pain sometimes!