You will then recieve email for all new posts as they are posted. You can mute categories in your preferences and topics on the topic page if you get too much email. You can reply to the emails.
Some categories allow you to post new topics by email as well. Look for info in the category description. This is configured for categories that are replacements for old high traffic mailing lists only. New categories will not get this option.
Yes, please feel free to organise this as you feel is best. It might be a
good idea to have it very visible now in the beginning though, when we hope
a lot of people will be migrating.