Quando se encontram, as duas amigas abraçam-se e beijam-se.

Here, se means each other.

Because the subject is plural — as duas amigas — the actions are understood as reciprocal:

• se encontram = meet each other / meet
• abraçam-se = hug each other
• beijam-se = kiss each other

So this is not reflexive in the sense of they hug themselves. It is reciprocal: they do these things to one another.

This is a very important feature of Portuguese clitic pronouns.

In Quando se encontram, the word quando attracts the pronoun, so se comes before the verb. This is called proclisis.

In the main clause, as duas amigas abraçam-se e beijam-se, there is no word attracting the pronoun, so in standard European Portuguese the normal position is after the verb. This is called enclisis.

So:

• Quando se encontram → se before the verb
• abraçam-se / beijam-se → se after the verb

This difference is especially important in European Portuguese.

In standard European Portuguese, no — Quando se encontram is the correct form.

The conjunction quando triggers proclisis, so the pronoun should come before the verb.

So:

• correct: Quando se encontram
• not standard here: Quando encontram-se

Because when an unstressed pronoun such as me, te, se, nos, vos, lhe, lhes comes after the verb, Portuguese spelling uses a hyphen.

So:

• abraçam-se
• beijam-se
• levantam-se
• chama-se

This is standard spelling for enclisis.

In this sentence, se encontram means meet or meet each other.

The verb encontrar can mean to find, but encontrar-se very often means to meet.

So in context:

• Quando se encontram = When they meet
• not When they find themselves

The plural subject makes the reciprocal meaning clear.

They are in the present indicative:

• encontram
• abraçam
• beijam

This tense is used here for a general or habitual action:

• Quando se encontram, ... = Whenever / When they meet, ...
• abraçam-se e beijam-se = they hug and kiss each other

It describes what normally happens.

Because they are in the 3rd person plural of the present tense.

The subject is as duas amigas = the two female friends, which is plural, so the verbs must also be plural.

Examples:

• ela encontra = she meets
• elas encontram = they meet

Likewise:

• ela abraça / elas abraçam
• ela beija / elas beijam

Because Portuguese often leaves subject pronouns out when the subject is already clear.

Here, the subject is explicitly stated as as duas amigas, so elas is unnecessary.

Portuguese commonly does this:

• As duas amigas abraçam-se.
• Chegaram cedo.
• Somos estudantes.

In English, subject pronouns are usually required, but in Portuguese they are often omitted.

As duas amigas means the two female friends. The definite article as makes the phrase specific.

Portuguese often uses the definite article in places where English may not. Here it sounds very natural because we are talking about two specific friends already identifiable in the context.

So:

• as duas amigas = the two friends
• duas amigas = two friends

Both are possible in some contexts, but as duas amigas is more specific.

Because amigas is the feminine plural form, and the sentence is talking about two female friends.

Agreement works like this:

• amiga = one female friend
• amigas = more than one female friend
• amigo = one male friend / a male friend
• amigos = more than one male friend, or a mixed group

Since both friends are female, amigas is the correct form.

Yes, it is normal and appropriate.

Quando se encontram is an introductory subordinate clause, and Portuguese usually separates that kind of opening clause with a comma:

• Quando se encontram, as duas amigas abraçam-se e beijam-se.

This works much like English:

• When they meet, the two friends hug and kiss each other.

In standard European Portuguese, the most natural form here is abraçam-se e beijam-se.

Using se before the verbs in a simple affirmative main clause is not the normal default in European Portuguese unless something attracts the pronoun.

So for European Portuguese:

• more standard/natural here: abraçam-se e beijam-se
• less appropriate in this sentence: se abraçam e se beijam

This is one of the areas where European and Brazilian Portuguese often differ.

It can often suggest either, depending on context.

Because the verbs are in the present tense and the sentence describes a typical repeated action, English may naturally translate it as:

• When they meet, ...
• Whenever they meet, ...

Both can fit. The Portuguese sentence describes what usually happens on those occasions.