صديقي متطوع.

Because this is a nominal sentence in Arabic. In the present tense, Arabic usually does not use a separate word for is/am/are.

So:

• صديقي متطوع literally looks like my friend volunteer
• but it means My friend is a volunteer

If you wanted a past meaning, you would use a verb such as كان:

• كان صديقي متطوعًا = My friend was a volunteer

صديقي breaks down as:

• صديق = friend
• ـي = my

So صديقي means my friend.

There is no الـ because the suffix ـي already makes the noun definite. In Arabic, you do not normally combine الـ with a possessive suffix on the same noun.

So Arabic says:

• صديقي = my friend

not:

• الصديقي

Arabic has no separate indefinite article like English a/an. A bare indefinite noun can already mean a volunteer.

So:

• متطوع = a volunteer or simply volunteer, depending on context

In fully vowelled Arabic, the indefiniteness is often shown by tanwīn:

• مُتَطَوِّعٌ

But in normal unvowelled writing, you usually just see:

• متطوع

متطوع is an active participle derived from the verb تطوع meaning to volunteer.

Active participles in Arabic are very common and can behave like:

• a noun: a volunteer
• an adjective: volunteering or voluntary, depending on context

In this sentence, it is best understood as the predicate meaning a volunteer.

In صديقي متطوع:

• صديقي is the subject
  Arabic term: المبتدأ
• متطوع is the predicate
  Arabic term: الخبر

This is one of the most basic Arabic sentence patterns:

• subject + predicate

So a lot of simple present-tense statements work this way.

A fully vowelled version is:

صَدِيقِي مُتَطَوِّعٌ

A few notes:

• مُتَطَوِّعٌ has ـٌ because it is indefinite and nominative
• صَدِيقِي is also nominative as the subject, but with the suffix ـي the case ending is not visibly pronounced the same way; grammarians say its ending is estimated

For a beginner, the important thing is simply to recognize:

• صديقي = the subject
• متطوعٌ = the predicate in the nominative

A careful pronunciation is:

ṣadīqī mutaṭawwiʿ

You may also hear the fully inflected form as:

ṣadīqī mutaṭawwiʿun

Helpful breakdown:

• صديقي = ṣa-dī-qī
• متطوع = mu-ta-ṭaw-wiʿ

A few pronunciation points:

• ص is an emphatic s, heavier than normal English s
• ط is an emphatic t
• ع is the sound ʿayn, which has no exact English equivalent
• In pausal pronunciation, the final -un is usually dropped, so learners often hear mutaṭawwiʿ

No. صديقي متطوع is already a complete and natural sentence.

Adding هو is not necessary here. In MSA, an extra pronoun like هو may appear:

• for emphasis
• or in certain structures, especially when both sides are definite

But with an indefinite predicate like متطوع, the simple version is the normal one:

• صديقي متطوع

Yes, depending on context, active participles can sometimes describe a current state or ongoing role.

So متطوع can suggest ideas like:

• a volunteer
• volunteering
• someone who volunteers

In this short sentence by itself, the most natural understanding is usually:

• My friend is a volunteer

But context can make it feel more like:

• My friend volunteers

For a simple neutral statement, the normal order is:

• صديقي متطوع

That is the best pattern for learners to use.

Arabic can sometimes move parts of the sentence around for emphasis or style, but in basic MSA, subject first, predicate second is the safest and most natural choice here.

You would usually make both words feminine:

صديقتي متطوعة

This breaks down as:

• صديقتي = my female friend
• متطوعة = female volunteer

So the predicate changes to match the gender of the person being described.