You need to send all the forms included in the checklist for the Sponsor, and the Principal Applicant and mail them TOGETHER. Check out the CIC website at
http://www.cic.gc.ca/english/immigrate/sponsor/spouse-apply-how.asp Easiest way is to click on your region (USA) and request an application package be mailed to you. This will include all the forms you need to fill out, and has to document checklist.
You need to request a criminal background check from both the FBI and any state that you have lived in longer then a year.
You can get the FBI information here
http://www.fbi.gov/hq/cjisd/fprequest.htm and the state information is available on the CIC website as well... or heck even just google it for each particular state ex) I googled Illinois criminal background check, and was brought to the appropriate Illinois state Police site. In your PR application, you need to include the letter that you recieve back from the FBI/State Police- indicating that you have no criminal record etc...
Both the FBI and each state charges a fee for requesting the background checks. Its different everywhere... so just look it up for whatever state(s) you are dealing with. Indicate on the envelope as well as on the request form that its for immigration purposes and what date you need it by. There is obviously no guarantees, and they can take anywhere from 2 weeks to 10 weeks to get back to you.
You still seem to have alot of questions- most of which can simply be answered in your application packet. Send away for that- read it all over a couple times and I am sure things will become a little more clear.