I slipped on some water in a store and landed on my knee; store manager said he submitted the incident. What do I do know?

If you decide to work independently with the store be prepared to do your homework and provide all the documentation you need to prove your case. Do not just settle immediately until you know the extent of your injuries.  People are often contacted by insurance companies to settle their cases for minimal amounts long before they know what their injuries really are.  Have you sought medical treatment for your injuries? And do you have bruises which should be photographed?  And were there any witnesses to the incident? What caused the "dirty" puddle to be there and how long was it there?  Let me say this...people are often shy of claiming for themselves what their lawyer would have no difficulty pursuing on their behalf.  That is why we have lawyers!

Well, typically you have choices.  You can choose to follow an internal process and negotiate directly with ACME corporate regarding this matter.  Do you have medical bills? Any bruising? Did you take pictures?

If you are asking if you should sue, that is up to you.  Should you choose to sue for physical injuries and pain and suffering, be prepared to prove your losses.  You can choose to negotiate directly with their insurance company or hire a lawyer to do so on your behalf.