What are the two elements every blessing must include?
Every blessing requires both: God's name (Hashem Eloheinu) and His kingship (Melech haolam). Missing either one invalidates the blessing — it must be repeated.
Question 2
What is a bracha l'vatala?
Bracha l'vatala: saying a blessing where one isn't required. The Rambam treats this as a Torah prohibition (taking God's name in vain). Great care is taken to avoid unnecessary blessings.
Question 3
If you answer "Amen" to someone else's blessing, what is the halachic effect?
Amen is a full form of participation. The Talmud (and Rambam) hold that answering Amen is equal to saying the blessing yourself. This is why Amen is such a powerful word.
Question 4
Can you answer Amen to your own blessing?
Amen is inherently a response — you don't answer Amen to your own blessing (except at the end of Birkat Hamazon where it's a known custom). Amen means: "I affirm what you said."
Question 5
What words are added to a blessing for a commandment (not said for food)?
Blessings on commandments add: "asher kidshanu b'mitzvotav v'tzivanu" — affirming that the mitzvah comes from God's sanctification and command. Food blessings don't include this addition.