I'm not sure what you mean by "another email from my own email account." Are you replying to an email you yourself sent to your account, from another account of yours perhaps ? Or are you replying to another person's email to you ?
In any case, if you're unfamiliar with sending emails: you simply choose the email you want to reply to, i.e. select it either by putting a check in the box to the left of it in the message list or by clicking on the email message itself, which will open the message for viewing. Then click the "Reply" button which will be above (and maybe also below) the message or message list. Double-check that the address already in the "To" field is the one you want and be sure to remove any additional addresses that may be present in the "To" or "CC" boxes. Then just put your cursor in the text window (if it's not blinking there already) and type your reply.
Please, clarify if this isn't what you were asking about.