Kuorin mandariinin keittiössä ja annan osan siskolleni.

Finnish often leaves out subject pronouns when the verb ending already tells you who is doing the action.

• kuorin = I peel
• annan = I give

So Minä kuorin mandariinin... is possible, but minä is usually unnecessary unless you want emphasis or contrast.

Here mandariinin is the object form used for a single, complete object. In Finnish grammar this is often called the total object. In the singular, it often looks the same as the genitive.

So:

• Kuorin mandariinin = I peel the whole mandarin
• Kuorin mandariinia = I am peeling mandarin / some mandarin / the action is incomplete or unbounded

Plain mandariini would not be the normal object form here.

Keittiössä means in the kitchen.

It comes from:

• keittiö = kitchen
• -ssa / -ssä = the inessive case, meaning in

So:

• keittiö = kitchen
• keittiössä = in the kitchen

This is because of vowel harmony.

Finnish case endings often have two versions:

• back-vowel version: -ssa
• front-vowel version: -ssä

Since keittiö contains the front vowel ö, it takes -ssä.

Compare:

• talossa = in the house
• metsässä = in the forest
• keittiössä = in the kitchen

Osan comes from osa, which means part or piece.

So annan osan literally means I give a part or I give a piece. In this sentence, it is naturally understood as part of the mandarin.

This is the same object-case idea as with mandariinin.

• annan osan = I give a whole piece / a complete part
• annan osaa = I give some part of something in a more unbounded or incomplete sense

In this sentence, the speaker is giving a definite piece, so osan is the natural choice.

Finnish often leaves that kind of thing understood from context.

Because the first part of the sentence mentions the mandarin, osan is naturally understood as part of it.

If you want to say it explicitly, you can add it:

• annan siskolleni osan mandariinista = I give my sister part of the mandarin

Here mandariinista literally means from the mandarin.

Siskolleni has three parts:

• sisko = sister
• -lle = to someone, the allative case
• -ni = my

So:

• siskolle = to the sister / to a sister
• siskolleni = to my sister

After antaa meaning to give, the recipient is usually put in this -lle form.

Because -ni already means my.

So siskolleni already contains the idea to my sister.

You can say minun siskolleni, but then minun adds emphasis or extra clarity. In standard Finnish, the possessive suffix alone is often enough.

Yes. Finnish word order is flexible, and this sentence is perfectly normal.

A basic pattern is often Subject–Verb–Object, but since the subject minä is omitted, you get:

• Kuorin mandariinin keittiössä
• ja annan osan siskolleni

Finnish changes word order mainly for emphasis. For example:

• Keittiössä kuorin mandariinin = emphasizes in the kitchen
• Siskolleni annan osan = emphasizes to my sister

Yes. Both are present tense forms:

• kuorin = I peel
• annan = I give

In Finnish, the present tense can cover several meanings that English sometimes separates:

• something happening now
• something habitual
• sometimes even near future

In this sentence, the most natural reading is a present action.

Finnish has no articles. There is no direct equivalent of English a or the.

That means words like mandariinin, osan, and siskolleni do not automatically tell you a or the the way English does. Context gives that information.

So depending on context, mandariinin could be translated as:

• a mandarin
• the mandarin

English has to choose an article, but Finnish usually does not.