Post la duŝo mi brosas miajn harojn.

In Esperanto, haro means one hair, and haroj means hair in the everyday sense of the hairs on your head. So mi brosas miajn harojn is the normal way to say I brush my hair.

If you want a more collective word, Esperanto also has hararo, meaning a head of hair or someone’s hair as a whole.

Because miajn harojn is the direct object of brosas. In Esperanto, direct objects take -n.

Also, words that describe a noun must agree with it. So:

• haroj = hairs / hair
• harojn = hairs / hair as a direct object
• miaj haroj = my hair
• miajn harojn = my hair as a direct object

So the -n appears on both the possessive adjective and the noun.

Because miaj would only be plural, not accusative. Here you need both plural and direct-object marking:

• miaj = my
• miajn = my, plural + direct object

Since harojn is plural and has -n, miajn has to match it.

Because sia/siaj/siajn is only used when the subject is third person: li, ŝi, ĝi, ili, or a noun like la knabo.

So:

• Mi brosas miajn harojn. = I brush my hair.
• Ŝi brosas siajn harojn. = She brushes her own hair.

With mi, you use miajn, not siajn.

Because a possessive like mia, via, or ŝia already makes the noun definite. In other words, my hair is already specific, so Esperanto normally does not add la.

That is why miajn harojn is natural, not la miajn harojn.

-as is the present tense ending in Esperanto. It can express a general habit, a usual action, or something happening now, depending on context.

Here it most naturally means something like a routine:

After the shower, I brush my hair.

Literally, it means after the shower:

• post = after
• la duŝo = the shower

In this sentence, it most likely means after showering or after I take a shower.

La is used because the speaker means a specific, identifiable shower event: the shower they have just taken, or the usual shower in that routine.

So post la duŝo is a very natural way to say after the shower.

Yes. Duŝado means showering as an activity or process.

So:

• post la duŝo = after the shower
• post duŝado = after showering

Both are understandable. Post la duŝo sounds very everyday and natural in this kind of sentence.

Yes. Esperanto word order is fairly flexible.

These are both fine:

• Post la duŝo mi brosas miajn harojn.
• Mi brosas miajn harojn post la duŝo.

The first version puts the time expression first, a bit like After the shower, I brush my hair in English.

The letter ŝ is pronounced like English sh. So duŝo is roughly DOO-sho.

A few other useful sounds from this sentence:

• j sounds like English y
• oj sounds roughly like oy
• harojn is roughly ha-ROYN

So the sentence sounds approximately like:

post la DOO-sho mi BRO-sas MEE-ayn ha-ROYN