How do you learn to use Twitter?

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How do you learn to use Twitter? I am new and am just now figuring this out. Basically, I'm trying to figure out if there is a way to schedule tweets. Sometimes I have several things to say but I don't want to send a mass of tweets all at once. Can you suggest any sites or programs that make things simple to understand? Also, I have already gotten several followers. Do I need to tweet everyone back when they choose to follow me. Thanks in advance for your help. Happy tweeting!