Hi daurelie

I would heartily recommend a dictionary called "The Plain English Dictionary" - I only have a UK edition http://www.amazon.co.uk/exec/obidos/ASIN/0003750566/026-1053936-5664451 but you may be able to find an equivalent.

A friend bought it for my 10 year old and I think its brilliant! It skips all the clever etymology stuff (you can find that elsewhere) and goes straight for a really clear definition and a sentence showing how the word is used.

There is a thread somewhere in this lot with on-line dictionaries which may be useful. Other than that just keep trying things out, you may be no less wrong than anyone else!