Sebelum berbelok, Ibu selalu melihat spion dan menyalakan sein.

Not necessarily. Ibu can mean mother, but in everyday Indonesian it is also a polite way to refer to an adult woman, similar to Mrs., ma’am, or simply the woman/lady depending on context.

So in this sentence, Ibu could mean:

• Mother/Mom, if the context is about someone’s mother
• a woman / Mrs. ..., if it is just referring politely to an adult female subject

Belok is the basic word related to turning.
Berbelok uses the prefix ber-, which often makes a verb intransitive, meaning the subject does the action without a direct object.

So:

• belok = turn / a turn
• berbelok = to turn

In this sentence, berbelok is natural because the subject is performing the action of turning.

Sebelum means before. It introduces a time clause:

• Sebelum berbelok = Before turning

It tells you when the main action happens. The main action is:

• Ibu selalu melihat spion dan menyalakan sein
  = she always checks the mirror and turns on the signal

So the structure is:

• Before turning, ...

Indonesian often omits the subject in a subordinate clause when it is clearly the same as the subject in the main clause.

So:

• Sebelum berbelok, Ibu selalu ...
• Sebelum Ibu berbelok, Ibu selalu ...

Both are understandable, but the first is more natural because the subject is already clear. English does something similar in phrases like Before turning, she...

The comma separates the introductory time clause from the main clause.

• Sebelum berbelok, = introductory clause
• Ibu selalu melihat spion dan menyalakan sein. = main clause

This is similar to English writing:

• Before turning, she always checks the mirror and turns on the signal.

In Indonesian, punctuation can sometimes be flexible, but the comma here is normal and helpful.

Selalu means always. It is an adverb of frequency.

In this sentence:

• Ibu selalu melihat spion dan menyalakan sein
• literally: She always looks at the mirror and turns on the signal

Its position before the verbs is very natural. It shows that this is a habitual action, not something happening just once.

Melihat is usually a transitive verb, so it commonly takes a direct object:

• melihat spion = look at the mirror / check the mirror

This is very natural in Indonesian.

You may also hear melihat ke ... in some contexts, but melihat spion is the more standard and direct phrasing here. It treats spion as the object of the verb.

Spion means a vehicle mirror, such as a rear-view mirror or side mirror. In everyday Indonesian, it usually refers to the mirror used while driving.

A few notes:

• It is a very common everyday word
• It is a loanword
• In context, it does not mean a household mirror

So melihat spion means checking the driving mirror(s).

Menyalakan means to turn on / switch on / light up.
Sein means a turn signal / indicator.

So:

• menyalakan sein = to turn on the turn signal

Literally, it is something like switch on the indicator.

The base word is nyala, which relates to being on, lit, or burning.

With the prefix meN- and suffix -kan, it becomes menyalakan, which usually means to cause something to be on or to switch something on.

Compare:

• lampunya menyala = the lamp is on
• dia menyalakan lampu = he/she turns on the lamp

So in your sentence:

• menyalakan sein = turn on the signal

Because both verbs share the same subject, Indonesian does not need to repeat it.

• Ibu selalu melihat spion dan menyalakan sein
• literally: Mother / the woman always checks the mirror and turns on the signal

The subject Ibu applies to both:

• melihat spion
• menyalakan sein

This is the same as English:

• She checks the mirror and turns on the signal not
• She checks the mirror and she turns on the signal unless you want extra emphasis.

Sein is extremely common in everyday Indonesian, especially when talking about driving. It is perfectly normal in conversation.

Depending on context, you might also encounter more descriptive expressions like:

• lampu sein = turn signal light
• lampu isyarat belok = a more formal/descriptive version

But for normal speech, sein is the word most learners will hear very often.