British English and American English have significantly different vocabulary and usage. Do not assume that because you a proficient in British English that American English will be easy. For example, in American English the phrase “pass out” means to distribute or to lose consciousness, not the British English meaning of to graduate. Some words might even have completely opposite meanings. For example, “to table a measure” means to postpone consideration in the US, not to commence discussion, and “public school” means a school operated by the city or state government, not a private school. The word “school” can be used to refer to colleges and universities, not just grammar school. In American English the abbreviation “s.o.” stands for “significant other”, a spouse or girlfriend/boyfriend, not sex offender. Additional sets of confusable words can be found in the English-English Dictionary.
English usage among Americans will often differ from the grammar you learn from books. There are considerable dialectal variations across the country. Many Americans will not follow some of the prescriptive rules of grammar they learned in elementary school. Rules that prohibit split infinitives and ending a sentence with a preposition are often ignored. American English is an evolving language, not carved in stone.
When someone says “thank you”, the customary response is “you’re welcome”. “You’re welcome” doesn’t have the same meaning as in British English.
You will find it handy to carry a small pocket dictionary with you. There is also a free American English dictionary and thesaurus on the web. Google’s “define:” keyword can be used to look for definitions on the web. For example, use define:scholarships to search for the definition of the word ‘scholarships’. NTC publishes a series of books about American idiomatic expressions, which you can find in most large bookstores. You will find these books helpful.
For a dictionary of words related to financial aid and admissions, please look at this site’s glossary.