Learn Hardcore Turkish: Dışarı çıkmadan giyin; şarj kablosunu da unutma. - Get dressed before going out; don’t forget the charging cable.

Both readings are possible. In practice, with preparatory actions, -madan commonly means “before” (i.e., “Get dressed before you go out”). If you want to make “before” explicit and unambiguous, say çıkmadan önce.

Why is it dışarı, not dışarıya?

Both exist:

dışarı çıkmak is the default idiom (“to go outside”).
dışarıya çıkmak also works and slightly emphasizes direction “to the outside.” Here, dışarı is the most natural.

Why is it giyin and not giy?

giyinmek = to get dressed (no object). Imperative 2nd singular is giyin.
giy- = to put on/wear a specific item (takes an object): Montunu giy (“Put on your coat.”) Since the sentence is about getting dressed in general, giyin is the right verb.

What person and politeness level is giyin?

It’s the 2nd person singular imperative (informal “you”). Polite or plural forms:

2nd person plural/informal to a group: giyinin
Polite singular or plural: giyininiz (or simply giyinin in modern usage)

Why is a semicolon used here? Could I use something else?

The semicolon neatly links two related imperatives. You could also use:

A period: … giyin. Şarj kablosunu da unutma.
A comma (less formal): … giyin, şarj kablosunu da unutma.
Or a coordinator: … giyin ve şarj kablosunu da unutma.

What does da in şarj kablosunu da do?

Clitic da/de means “also/too” and attaches after the word it focuses. Here it adds the charging cable to an implied list of things not to forget. It’s unstressed: focus stays on şarj kablosunu.

Is this da the same as the locative suffix -da/-de?

No.

Clitic da/de (“also”) is written separately, follows the focused word, obeys vowel harmony (da after back vowels, de after front), and its “d” never turns into “t.”
Locative suffix -da/-de is attached to the noun (e.g., evde “at home”).

Why is it şarj kablosunu with -u at the end?

That’s the definite accusative marking the direct object as specific/definite: şarj kablosu → şarj kablosunu (“the charging cable”). With a non-specific reading you’d leave off the accusative, but here a particular item is meant.

Why kablosunu and not kabloyu?

Because şarj kablosu is a noun–noun compound (an “indefinite possessive” compound). The head noun takes the 3rd person possessive -su/-sü: kablo → kablosu. When you then mark it definite accusative, it becomes kablosunu. Saying şarj kabloyu is ungrammatical for this compound.

Can I replace şarj kablosunu with a pronoun?

Yes: Onu da unutma (“Don’t forget it, either”). The clitic da still follows the focused element, so both onu da and, with a different nuance, onu da before/after other material are possible; keep da right after the word it emphasizes.

How is unutma formed, and what are the other imperative forms?

Verb: unutmak (“to forget”)
Negative imperative 2nd singular: unut-ma → unutma (“don’t forget”) Other forms:
2nd plural/polite: unutmayın
Very formal: unutmayınız Affirmative 2nd singular would be unut (“forget!”).

Is the sentence blunt? How can I make it more polite?

As-is, it’s informal and direct. To soften:

Add lütfen: … unutma lütfen.
Use polite plural: … unutmayın.
Combine both: … lütfen unutmayın.

How do you pronounce the tricky parts like şarj and the vowel ı?

ş = “sh” as in “shop.”
j = “zh” as in “measure.” şarj sounds like “sharzh.”
ı (dotless i) is a central vowel, like a relaxed “uh.” dışarı ≈ “dɯ-sha-rɯ.”
ç = “ch” as in “church” (so çıkmadan starts with “ch”).

Is çıkmadan alone enough, or should I say çıkmadan önce?

Both are correct. -madan alone is common and natural here. -madan önce makes the “before” meaning explicit and removes any “without” reading.

Can da go after the verb, like unutma da?

Yes, but it changes nuance. Unutma da can work as a softener or as part of a larger sequence (“…and don’t forget”). In your sentence, şarj kablosunu da unutma specifically marks the cable as the item being additionally remembered, which is the usual intent.

Are there common alternatives to şarj kablosu?

Yes:

şarj aleti = charger (the brick/adapter)
şarj cihazı = charger/device (more formal) If you literally mean the cable, şarj kablosu is precise.

Do I need a comma after dışarı çıkmadan?

Not required in such a short clause. You may add one for a slight pause (Dışarı çıkmadan, giyin), but it’s optional. The semicolon between the two imperatives is stylistic; a period works just as well.