Глагол "быть" в настоящем времени.

بسم الله الرحمان الرحيم

السلام عليكم ورحمة الله ، وبعد:

Well Ukhti, in Arabic to define something you could use those Pronouns and by translating the sentence or a definition to English or French we start our sentence by the verb "to be" (“être “ in French and its synonym in Arabic: kan, yakunu كان، يكون) to define what we want to explain and in this case you CAN NOT remove it, otherwise the sentence will NOT be correct grammatically or meaningfully! 

About  those Pronouns we’ve talked about ,seem to be called "Detached ~ الضمائر المنفصلة", but in this case we call them in Arabic Grammar “Detaching Pronouns ضمائر الفَصْل” and the deference between them that detaching Pronoun could be removed and our sentence /meaning would be always CORRECT! For ex: السعادة أن يكون لديك أصدقاء...   as you see in our example we removed هي and the meaning is still correct and Not like in Detached pronoun, to remove it that could make your sentence Meaninglessness , Wrong : for ex:

 هِيَ مَنْ كَتَبَتْ الدَّرْسَ (She's who wrote the lesson): we can't remove hiya هي pronoun otherwise the sentence would be wrong and missing something!

Another example as in famous Hadith of Jibril peace be upon him when He (peace be upn him) was asked what's Al-Iman (Faith) so He answered:  

 ..“الإِيمَانُ أَنْ تُؤْمِنَ بِاللهِ وَمَلَائِكَتِهِ، وَكُتُبِهِ، وَرُسُلِهِ، وَلِقَائِهِ، وَتُؤْمِنَ بِالْبَعْثِ الآخِرِ”

So we can add Huwa هو pronoun (Detaching~) between المُبْتدَأُ (Al-mubtada’ in this case الإِيمَانُ), translated as “Nominative Subject” and  الخَبَرُ  (Al-khabar in this case the verbal sentence «أَنْ تُؤْمِنَ بِاللهِ… » ), translated as “Nominative Predicate” and the meaning is always correct and same:

..“الإِيمَانُ هو أَنْ تُؤْمِنَ بِاللهِ وَمَلَائِكَتِهِ، وَكُتُبِهِ، وَرُسُلِهِ، وَلِقَائِهِ، وَتُؤْمِنَ بِالْبَعْثِ الآخِرِ”

والله أعلم.

Hope that you get the point and learnt something J

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Assa3da hiya...

Assalamu 3leikum!
I have noticed that when you see a definition of something in Arabic usually it followed by huwa and hiya which I understand as IS. PLease correct me if Im wrong.
From the picture below I understood that it means:

"Happiness is when you have crazy friends."

But I didnt understood what in this case means in yakun. Please give me some more examples with it.

Jazakum Llahu khairan in advance.
Take care :)

يكون is simply the present tense of كان 

كان = was (past form of verb to be)

يكون = to become / to be

so, أن يكون لديك lit. means "that is in your possession"