Have you opened up the amcas app? It will all make sense once you are actually on the form. You can start the app/look around in there without actually applying yet. You can save your work and go back into the system an unlimited number of times. To actually "apply" you would have to hit a submit button, and then the system will ask you to certify (i.e ask are you really, really sure about this). So no harm no foul in going in to look around so you can figure out your game plan.
And yes, for each entry, you must provide dates, a contact person's name/phone/email, hours per week (you can estimate conservatively if you never kept track). For entries that obviously would not have hours, such as awards, its fine to leave the hours box blank.
You can enter up to 15 work/volunteer experiences, hobbies, awards, honors. Really anything you have done other than coursework (which will go in a different section).