Se vi kunportus poŝlampon dum ĉiu vojaĝo, vi sentus vin pli sekura nokte.

The ending -us is the Esperanto conditional mood. It is used for something hypothetical, imagined, or dependent on a condition.

So this sentence is an if ... would ... type of sentence:

• Se vi kunportus ... = If you were to bring / if you brought ...
• vi sentus ... = you would feel ...

In Esperanto, this kind of unreal or hypothetical condition commonly uses -us in both parts.

Kunportus comes from:

• porti = to carry
• kun- = with, along

So kunporti means to bring along, to take with you, or to carry with you.

That is a little more specific than just porti, which can simply mean carry or wear depending on context.

The -n ending marks the direct object.

Here, the thing being brought along is the flashlight:

• vi kunportus poŝlampon = you would bring along a flashlight

So poŝlampon gets -n because it is the object of kunportus.

Also, poŝlampo is literally pocket-lamp, which is the normal Esperanto word for flashlight.

In Esperanto, senti is often used with a pronoun when talking about how someone feels:

• Mi sentas min laca. = I feel tired.
• Vi sentus vin pli sekura. = You would feel safer.

Literally, this is something like you would feel yourself safer, but in normal English we just say you would feel safer.

So vin is there because the sentence is using the pattern senti + pronoun + adjective.

Because sin is only used for the third person.

Use sin when the subject is things like:

• li
• ŝi
• ĝi
• ili
• a noun, such as la viro

But here the subject is vi, so the correct form is vin, not sin.

Compare:

• Vi sentas vin feliĉa.
• Li sentas sin feliĉa.

Because sekura is an adjective describing the person's state, while sekure would be an adverb describing how an action is done.

Here the meaning is:

• you would feel safer
• not you would feel safely

So Esperanto uses the adjective:

• senti vin sekura = feel safe

If you used sekure, it would change the grammar and sound wrong here.

Because sekura here is not a normal adjective directly attached to vin the way an attributive adjective would be. It is a predicate adjective after senti.

In other words:

• vin is the object pronoun
• sekura describes the state you would be in

This is the normal pattern in Esperanto:

• Mi sentas min bona.
• Ŝi trovis sin sola.
• Vi sentus vin pli sekura.

So sekura stays without -n.

Pli means more, so pli sekura means more safe, which in natural English is safer.

The thing being compared does not have to be stated explicitly. It is understood from context.

So vi sentus vin pli sekura means:

• you would feel safer
• usually understood as safer than if you did not bring a flashlight

This works the same way as in English, where the comparison is often left unstated.

Because ĉiu means each or every, and it normally goes with a singular noun:

• ĉiu vojaĝo = each trip / every trip

If you use ĉiuj, that is plural:

• ĉiuj vojaĝoj = all trips

Both are possible in Esperanto in the right context, but dum ĉiu vojaĝo is the most direct way to say during every trip or on each trip.

Because dum is a preposition, and after a preposition you normally do not add -n.

So:

• dum ĉiu vojaĝo = during each trip

The -n is not needed because dum already shows the time relationship.

Esperanto often makes time adverbs by adding -e to a time-related root:

• tage = by day, during the day
• nokte = at night
• somere = in summer

So nokte is a very natural, compact way to say at night.

You could sometimes use a longer phrase in other contexts, but nokte is the usual choice here.

Not completely. Esperanto word order is fairly flexible because endings show the grammatical roles.

This sentence has a very natural order:

• Se vi kunportus poŝlampon dum ĉiu vojaĝo, vi sentus vin pli sekura nokte.

But some parts could move for emphasis, for example:

• Se vi dum ĉiu vojaĝo kunportus poŝlampon, vi sentus vin pli sekura nokte.
• Nokte vi sentus vin pli sekura, se vi kunportus poŝlampon dum ĉiu vojaĝo.

The original version is simply the most neutral and straightforward.