Echoes are also known as conferences or sub areas. Local echoes are only on one or two bbs's in a given area. Another type of local area might be a User Chat or Forum area. This one is only readable by users of that system, and is usually a place where one user can leave another user a message. A regional echo is an echo that is carried only in one net or region.
Many nets have echoes for chatting and so forth.
Your sysop can point these out to you. Most international echoes use the English language as a standard language. You could find yourself in trouble posting in a foreign language. Echo rules or guidelines are usually posted monthly, or more often. Moderators are generally either the originator of a conference, appointed by the originating moderator, or elected democratically on the echo.