First, you'll need to make sure that the state Board of Nursing (BON) where you are applying will accept your Canadian nursing degree. Not all of them will.
When you want to take the NCLEX, you need to first apply to the state BON. You'll need to send several paperwork items, including information for a background check, money to pay the application fee, transcripts from your school, and a letter from you school that states you completed the program. The state BON will process your application and approve or deny you to take the test. Depending on the state you are registering in, this can take up to two months or longer.
You also need to register with Pearson VUE. This is the company that administers the NCLEX. The test is taken on the computer at one of the many approved testing centers throughout the country. You can take the NCLEX at any site, but you have to specify where you will take it when you register. The fee for the NCLEX exam is 200 dollars (separate from the application fee for the state BON).
Once your application is approved by the state BON, they will notify Pearson VUE and you will receive an ATT (authorization to test) number. You need this to schedule your exam. Depending on when you apply or what state you are in, you may have to wait a couple of weeks to get an available testing day.
Then you go and take the NCLEX. The test uses something called "Computer Adaptive Testing." This means that your test is analyzed and adjusted as you go along. If you answer questions correctly, you get harder questions. If you answer wrong, you get easier ones. There is a minimum competency that you must meet in order to pass the test. The minimum questions that you can get is 75. The maximum is 265. When the computer determines that you are well above or well below the minimum passing standard then the test will shut off. NCLEX tests questions are divided into categories. You will get a certain number of questions from each category and you have to be above the passing standard in each category. The categories are: Safety, Health Promotion, psychosocial and physiological. The "medical" questions (such as pathophysiology, medication administration, nursing interventions, etc) are the majority of the test.
The results of your exam are automatically sent to your state BON. Some states participate in "quick results" which allow you to pay a fee to Pearson VUE to see your unofficial results after 48 hours. However, your state BON will finalize you application and give you your official license. The time it takes for this to occur can be a few days or several weeks. If your state does not have quick results, then you will need to wait for notification from the BON to see if you passed or not.
Kaplan review books, Saunders, and LaCharity are very popular and reliable resources for NCLEX review. The content is essentially the same as what you learned in Canada, but there may be some differences in what you are allowed to do (scope of practice) and the NCLEX style questions may be different. So the most important things you can do are review the USA nurse's scope of practice and answer lots of NCLEX style practice questions. Kaplan test taking strategies can give you some helpful hints about how to answer NCLEX questions.
I would give yourself a few weeks, at least, to study for the NCLEX, especially if you aren't familiar with the style of questions. However, it will be at least a month after you apply to take the NCLEX before you are actually able to sit for it. As long as you are studying during that time you be well prepared.