Icelandic main clauses are V2 (the finite verb is in second position). The order here is:
það is a dummy or expletive subject (like English “it” in “it is cold”). Icelandic generally requires a subject, especially in weather/ambient statements: það er kalt, það rignir, það er myrkur.
You can sometimes omit það in a stylistic way (e.g., þegar dimmt er), but the neutral, everyday form includes það: þegar það er myrkur/dimmt.
All of these are idiomatic:
A handy order for main clauses is: Subject – finite verb – sentence adverbs – ekki – verb particles/directional adverbs – objects/PPs – time.
Examples:
út here is a directional adverb/particle. To specify direction with a destination or source, combine it with a preposition:
Be careful with út af: it often means “because of” or “off (down) from,” not simply “out of.”
Primary stress in Icelandic is on the first syllable of words.
Við is the nominative subject form (we). Okkur is the object/dative form (us). Subjects normally appear in the nominative in Icelandic, so you need við with förum: