English is not one of the easy languages. There are many reasons for this, not least of which is our spelling, which makes our language (or languages, if you prefer), not only troublesome for foreigners, but tricky for us, too.
In contrast to the romance languages that I translate from, English words frequently select their denotations not only from syntactic modifiers but also from context. Um... in plain English please.
In English, the meaning of a word can be changed not only by the words next to it in a sentence, but also by the situation being described. Examples:
The verb to get is one of my favourite words in any language*. On its own, to get is to obtain or acquire. Consider what happens when you add the preposition on to it:
The cat got on the table.
In this example, to get on is to change physical position, to a position where you are on top of something.
I'm getting on in plastics.
In this example, to get on is to advance your career. In plastics? A little outmoded isn't it?
I'm getting on with my homework.
In this example, you're doing what you are meant to do, rather than procrastinating.
Each time you change the context (cat, plastics, homework), you change the meaning of to get on.
This feature of English - present in other languages but by no means as common** - can make English both very tricky but also very rewarding. When you studied English at school, it is a pretty safe bet that your teacher encouraged you to avoid get, and employ something more explicit or more interesting instead (see my previous post on "said"). They may even have tried to encourage you to vary your vocabulary for variation's sake. In writing, this is not a good thing. English reads better if you take advantage of the metamorphic nature of words like get, and only use something more specific when you really need it.
In their defence, I don't think your teachers were wrong to tell you to do it, but they should have told you that the purpose of the exercise was to expand your vocabulary, but that slavishly trolling the thesaurus is not how to write good prose.
* my absolute favourite word is causa in Latin. That is how much of a geek I am.
** feel free to cite examples of languages that I don't know where this is as common as in English; I'd love to know.