If there is a discussion going on that you are very interested in and want to know when someone has replied to a post of yours or someone else has followed up you can set Notification preferences to get an alert by email - immediately, daily or weekly as you prefer.
Follow the steps below, clicking on Profile in the main menu bar, then Edit Profile in your own Profile area, then selecting notifications from the range of tabs.
There are many settings for Notifications but I have just chosen some of the key areas that you may be interested in. As you can see, there is a drop-down box beside each choice and you can set that as anything from Never up to Instantly. The email you receive will be headed up with the type of notification you requested ("A thread you created has been replied to") and will continue a clickable link that will take you to the forum where you can log in and read the comment as normal.