Maðurinn er í húsinu.

Because Icelandic usually expresses the with a suffix on the noun (a “postposed definite article”), not with a separate word.

• maður = a man / man
• maðurinn = the man Here -inn is the masculine singular nominative definite ending.

It’s nominative (the usual case for the subject of a verb like er = is). You can tell because:

• It’s the subject doing the “being.”
• Many Icelandic sentences have the subject in nominative unless a verb or construction requires something else.

Because í changes meaning depending on case:

• í + dative = location (in / inside, “being somewhere”)
• í + accusative = motion into (into, “going somewhere”) This sentence describes location, so it uses dative: í húsinu.

It’s hús (a neuter noun meaning house) in:

• dative singular (húsi)
• plus the definite ending (-nu) So: húsi + nu → húsinu = in the house (with í).

You’d remove the definite endings:

• Maður er í húsi. = A man is in a house. (That’s grammatically fine; context decides whether it sounds natural.)

Not in the same way as English. The most common way is the suffix:

• maðurinn, húsið, húsinu, etc. There is also a separate demonstrative-like form hinn in certain styles, but for everyday the, the suffix is the default.

Often it looks English-like in simple statements: Subject + verb + rest. But Icelandic is also flexible: you can move phrases to the front for emphasis, while keeping the verb early:

• Í húsinu er maðurinn. = In the house is the man. This is common when you want to emphasize the location.

Yes, vera (to be) conjugates:

• ég er = I am
• þú ert = you are (singular)
• hann/hún/það er = he/she/it is
• við erum = we are
• þið eruð = you are (plural)
• þeir/þær/þau eru = they are Here the subject is singular (maðurinn), so er is correct.

Different noun classes decline differently.

• maður is masculine with more visible changes across cases and definiteness.
• hús is neuter and has fewer changes in some forms, but it still declines: hús (nom/acc), húsi (dat), húss (gen). Adding definiteness gives forms like húsið, húsinu, etc.

A common way is yes/no question word order (verb first):

• Er maðurinn í húsinu? = Is the man in the house? You can also ask where:
• Hvar er maðurinn? = Where is the man?

Icelandic generally does not drop subjects the way Spanish or Italian does. You normally keep an explicit subject:

• Maðurinn er í húsinu. You can omit it only in limited contexts (commands, fragments, or when it’s clearly implied), but a normal full statement keeps it.