Það er auðveldara að læra þegar við deilum glósum og hjálpum hvert öðru.

Here það is a dummy subject, just like English it in It is easier to learn...

So:

• Það er auðveldara að læra... = It is easier to learn...

Icelandic often uses this pattern with an adjective plus an infinitive phrase. You could also say Að læra er auðveldara... but Það er auðveldara að læra... sounds very natural and common.

Auðveldara is the comparative form of auðveldur:

• auðveldur = easy
• auðveldari / auðveldara = easier

In this sentence, it means easier.

The form is neuter singular, which is common when the adjective refers to a whole idea or clause, such as að læra (to learn) or when it appears with dummy það.

So the structure is basically:

• Það er auðveldara... = It is easier...

Að læra is the infinitive of the verb læra (to learn).

• læra = learn
• að læra = to learn

Here it works like the English infinitive in It is easier to learn.

So the sentence has this core pattern:

• Það er auðveldara að læra = It is easier to learn

The word að is the normal infinitive marker, like English to.

Þegar means when here.

It introduces the time clause:

• þegar við deilum glósum og hjálpum hvert öðru
  = when we share notes and help each other

So it connects the idea it is easier to learn with the situation in which that is true.

Because þegar introduces a subordinate clause.

In Icelandic, main clauses often show verb-second word order, but subordinate clauses usually have a more straightforward order:

• þegar við deilum...
• when we share...

So after þegar, it is normal to have:

• conjunction + subject + verb

That is why við deilum is the expected order here.

Because they are both present tense, 1st person plural forms:

• við deilum = we share
• við hjálpum = we help

The subject við means we, and both verbs agree with it.

Their dictionary forms are:

• deila = to share
• hjálpa = to help

So this is a good example of how Icelandic verbs change according to person and number more clearly than English verbs usually do.

Because glósum is the dative plural form of glósa (note, usually study note).

• glósur = notes (nominative plural)
• glósum = notes (dative plural)

The reason for the dative is that the verb deila commonly takes the thing shared in the dative:

• deila glósum = share notes

So the form is determined by the verb.

Because Icelandic often leaves nouns indefinite in general statements.

Here glósum means something like:

• notes
• our notes
• study notes

depending on context.

If you wanted to make it clearly definite, you could use the suffixed article:

• glósunum = the notes

But in a general sentence like this, plain glósum is very natural.

Hvert öðru means each other.

So:

• við hjálpum hvert öðru = we help each other

This is a reciprocal expression. It is best learned as a unit rather than translated word-for-word.

An important point is that hjálpa takes the dative, and that affects the form of the expression here.

Also, Icelandic does not normally use a simple object pronoun for this meaning. For example:

• við hjálpum okkur would mean something more like we help us/ourselves, not the normal reciprocal we help each other

Because deilum and hjálpum are not infinitives. They are both finite verbs inside the same clause introduced by þegar.

So the structure is:

• þegar við deilum glósum og hjálpum hvert öðru

Here, við is the shared subject for both verbs:

• við deilum
• (við) hjálpum

The only að in the sentence belongs to the infinitive að læra.

Yes, that is grammatical.

Compare:

• Það er auðveldara að læra þegar...
• Að læra er auðveldara þegar...

Both mean basically the same thing.

The version with það er is especially common and natural, much like English It is easier to learn... The version starting with Að læra... can sound a little more direct or slightly more formal, depending on context.