The basic interrogative words, or question words (Who, What, Why etc.) are very useful in forming sentences, so let's take a look at them. I've split them into sections so it isn't just a massive wall of unfamiliar words, however there is some new vocabulary in this for you to learn. Don't worry about any of the verb endings at this point, as you will learn those in detail in later lessons.
Man? = What? Who?
Man te? What is it? Who is it? Man sa? What is that? Who is that? Man i lû? What (is) the time? Man sad? What place? (alternative for 'Where?') Man agoreg? What did you do? Man na i fen? Who is at the door?
Alternative To avoid ambiguity when asking 'Who is it?' you could also ask Man pen? What person? (Who?)
'Man' is the only attested Sindarin interrogative. Manen, Mas and Mar are all borrowed from Quenya and 'Sindarinised'.
Mas? = Where?
Mas agoreg? Where did you do that? Mas i adab? Where is the house? Mas i ada gîn? Where is your father? Mas le? / Mas ci? Where are you? Remember you've already seen this one before inLesson 3 - Mas dorthog?
Alternative Vi man sad? In what place?
Mar? = When?
Mar agoreg? When did you do that? Mar ci onnen? When (were) you born? Mar iavas? When is autumn? Mar telithar? When will they come?
Alternative Na van lû? At what time?
Manen? = How?
Manen agoreg? How did you do that? Manen istog? How do you know? Manen men hirnenog? How did you find us?
Amman? = Why? (For what?)
Amman agoreg? Why did you do that? Amman i eil luin? Why is the sky blue?
Amman theled? = For what purpose? (Why?)
Personally I prefer to use this one for its literal meaning of 'For what purpose' rather than 'Why', as there is a shorter version, as above.
Amman theled agoreg? Why did you do that? (For what purpose did you do that?) Amman theled anírog istol? Why do you want to know? (For what purpose do you want to know?)
Amman was reconstructed using the preposition an = to/for + man = what. You will learn about prepositions in Lesson 13.
Man i lû? What is the time? O van? From what? About what? Be van? According to whom? Ned var? During when?
There are many other questions you can ask when you combine the question words here with the prepositions in Lesson 13