From indicates who the message is from. You can sort your messages in order by who sent them by clicking on From. If the envelope looks opened, then you have read that message. Subject is where the subject line of the message is displayed. You can sort your messages by Subject.
Date is the date the E-mail was sent.
Most programs sort by Date as a default. If a message shows 1,234 K, then the message is very large and could take 10 - 15 minutes to download at normal 56k dialup speeds. In most cases, these large files are the cause of extended E-mail download times and can also result in disconnects. The small check boxes on the far left of the messages are used to mark when you want the message deleted. Then you have to click on the Delete feature to delete messages.