CNA or Certified Nursing Assistant is a first and the easiest to achive profession. To get it you need to pass CNA examination. Free practice exam is available on this site - http://cnaonline.info/cna-online-test-list/
Next level in nursing career is LPN or Licensed Practical Nurse. You can learn for LPN from the beginning no apply for CNA-to-LPN bridge programm. To get the license you need to pass national NCLEX-PN exam. Free practice NCLEX-PN exam is availaible at http://entrylevelmedical.com/lpn-online-practice-test
Another level in nursing career is RN or Registered Nurse. This is college or university degree. It takes much more time and learning to achieve. And has harder examination at the end - NCLEX-RN exam. You can also apply for bridge programs to get RN after CNA or LPN. Free practice NCLEX-RN exam is availaible at http://entrylevelmedical.com/rn-online-practice-nclex-rn-examination-free
All of those practice exams give you opportunity to save some money by better preparing for actual exam. And all of them are completely free. So dont't your chance and try tourself before applying for real paid exam.