يدفع صديقي اليوم.

Because Arabic often uses a verb–subject–object/time order, especially in Modern Standard Arabic.

So:

• يدفع صديقي اليوم = literally Pays my friend today = natural English: My friend pays today / My friend is paying today

You can also say:

• صديقي يدفع اليوم

That is also correct, but it puts a little more focus on my friend as the topic.

يدفع is a present-tense / imperfect verb, third person masculine singular.

Breakdown:

• يـ = marker for he
• دفع = root/pattern meaning to pay or to push

So يدفع means:

• he pays
• he is paying
• sometimes, depending on context, he will pay

In this sentence, the subject is صديقي (my friend), so the verb is in the he form.

Because صديقي means my male friend.

• صديق = a male friend
• صديقي = my male friend

So the verb must match that subject:

• يدفع صديقي اليوم = My male friend pays today

If you meant my female friend, you would say:

• صديقتي تدفع اليوم

Here:

• صديقتي = my female friend
• تدفع = she pays

It is made of:

• صديق = friend
• ـي = my

So:

• صديق = friend
• صديقي = my friend

This ـي is a possessive suffix attached directly to the noun.

In Arabic, possession is often shown by adding a suffix to the noun, instead of using a separate word like English my.

Examples:

• كتاب = book

• كتابي = my book

• صديق = friend
• صديقي = my friend

So Arabic does not need a separate word before the noun here.

اليوم means today. In this sentence, it functions as an adverb of time.

So the sentence structure is:

• يدفع = pays / is paying
• صديقي = my friend
• اليوم = today

Together: My friend pays today / My friend is paying today

That is just how the common Arabic expression works.

• يوم = day
• اليوم = today

Although الـ usually means the, in fixed time expressions like اليوم, the whole word is understood as today.

So learners should memorize اليوم as a very common time word meaning today.

It can mean both, depending on context.

The Arabic present/imperfect often covers:

• he pays
• he is paying
• sometimes he will pay

So يدفع صديقي اليوم could be understood as:

• My friend pays today
• My friend is paying today

The exact English translation depends on the context already given.

A common pronunciation is:

yadfaʿu

A rough breakdown:

• ya = like ya in yacht
• dfa = the d and f are both clearly pronounced
• ʿ = the letter ع, a deep throat sound with no exact English equivalent
• u = short u at the end in full pronunciation

So: yad-fa-ʿu

In normal unvocalized writing, the short vowels are not shown, so you see only يدفع.

Yes. The root is د-ف-ع.

This root often carries meanings related to:

• pushing
• driving away
• paying

So from the same root, you may see words related to payment or pushing/forcing something away. Learning roots helps you connect vocabulary more easily.

In fully formal Arabic grammar, yes, the sentence has case/mood endings, but in normal writing they are usually not shown.

A fully vocalized version could be:

• يَدْفَعُ صَدِيقِي الْيَوْمَ

Here:

• يَدْفَعُ has the indicative ending -u
• الْيَوْمَ is often accusative as an adverb of time, so -a

For صديقي, the noun has my attached with ـي, and that often hides the case ending in the written/pronounced form, so learners usually just read it as ṣadīqī.

At an early stage, it is enough to understand:

• يدفع = verb
• صديقي = subject
• اليوم = time expression

Yes. Arabic allows more than one correct order.

For example:

• يدفع صديقي اليوم
• صديقي يدفع اليوم
• اليوم يدفع صديقي

All can be correct, but the emphasis changes.

Very roughly:

• يدفع صديقي اليوم = neutral, more classical/written style
• صديقي يدفع اليوم = emphasizes my friend
• اليوم يدفع صديقي = emphasizes today

So word order in Arabic is flexible, but it is not random.

Because the verb itself already shows the person, number, and gender.

• يدفع already means he pays / he is paying

Then Arabic adds the explicit subject صديقي to say who that he is.

So Arabic often does not need a separate pronoun like هو unless you want extra emphasis or contrast.