Can I find log activity of who deleted a user and who edited an entry? Is there a 'latest greatest' tool that I can add that has ongoing logging of disable/enable and delete/update activity of users or entries, etc..?

Is there a good way to track this information before I add on a logging tool?  In other words, is this information somewhere in the mysql database anyways?

I know the current dashboard shows information related to entry creation, but, we have some new users that we are training and they have made some mistakes and we need to track those mistakes down.

thanks!
Craft only stores minimum audit information in the database... mainly just when a row was created and last updated.

If you're on Craft 2, there is a deprecated Audit Log plugin which might do what you're looking for.

I don't think the author has intentions of porting it to Craft 3, but there is a commercial plugin called Audit that is in the Craft Plugin Store.