I'm afraid that you are going to be disappointed. CRM itself does not explicitly record when someone logged in; CRM works as a web application that relies on Windows Authentication to allow users access so there is no actual logging in process as such (unless you are using CRM Online or a hosted CRM).
You could examine the web logs for IIS on the server that hosts your CRM web site. That might give you information as to when the CRM web site was accessed.
With regard to what people did, again no joy. CRM does not have an audit facility. There are third-party solutions for this or you could write your own add-on to track access. If you haven't already done this then the best you will be able to do is use the Modified By field that CRM maintains on a record to identify which records the user changed (and when) but that won't tell you what they changed.
