אֵ֥ת (et) is the direct-object marker in Biblical Hebrew. This is especially important in a language that is as flexible about word order as Hebrew is; without it, there wouldn't be a way to tell from grammar which noun in a noun-verb-noun construct is the subject and which is the object. (Context can disambiguate in many cases, but not all.) This word doesn't have a direct English translation; English doesn't have the concept.
You will see this word in other forms in the Tanakh too. (I apologize for not being able to type proper Hebrew here.) "Et" can combine with a possessive suffix; "oto" is "him", "otah" is "her", "oti" is "me", and so on. In that case, "et" isn't followed by another noun that is the object; it with its suffix is the object. (These same suffixes are used with other words too; this isn't specific to "et". For example, the word "im" means "with" -- and "imo" means "with him", "imi" means "with me", etc.)
One of your examples was
וְאֵ֥ת. This is the same word; in Hebrew, the vav prefix (vav is the first letter there) means "and" (or sometimes another conjunction). It is always a prefix; it does not stand alone. In the passage you quoted, there are two direct objects (the heaven and the earth); the "and" attaches to the "et" of the second phrase.
A good, accessible introduction to Biblical Hebrew that explains this well is The First Hebrew Primer. Don't be misled by the title; this is a book for adults, not children.
As for the hyphens, first, note that all punctuation was added long after the text was originally written, so while it's important, it's in a sense editorial. The punctuation added by the Masorites includes the trop, or cantillation, symbols, which specify both a melody to use when chanting the text and the internal punctuation (where are the commas, semicolons, and periods). There is one trop symbol per word -- but if not, if multiple words (mostly short, usually) are joined together in one musical "note", as it were, then those words are hyphenated in the text. "Et" is sometimes joined to the following word (the actual object), perhaps because of its specialized role, but it does not happen all the time.