Allah says further in the Holy Quran Chapter 2 Surah Baqarah verse 278:

O Believers!,  Fear Allah and give up that ‘riba’ which is still due to you,  if you are true believers.   But if you do not do so,  then you are warned of the declaration of war against you by Allah and His Messenger!

Allah says in the Holy Quran Chapter 4 Surah Nisa verse 161:

That they took ‘riba’,  although they were forbidden.  And that they devoured men’s substance wrongfully.   We have prepared for those among them who reject faith a grievous punishment (of Hell Fire)!

Allah says in the Holy Quran Chapter 2 Surah Baqarah verse 274-276:

But those who devour ‘riba’ become like the one whom Shaitaan has bewitched and maddened by his touch.   They have been condemned to this condition because they say,  “Trade is just like ‘riba”,  whereas Allah has made trade halaal and ‘riba’ haraam.   Henceforth,  if one abstains from taking ‘riba’ after receiving this admonition from his Lord,  no legal action shall be taken against him regarding the ‘riba’ he had devoured before:  his case shall ultimately go to Allah.   But if one repeats the same crime even after this,  he shall go to Hell,  where he shall abide for ever!   Allah deprives ‘riba’ of all blessing and develops charity,  and Allah does not like an ungrateful,  sinful person.

Al-Tirmidhi Hadith 2829        Narrated by Ali ibn AbuTalib

Ali heard Allah's Messenger (saws) invoke the curse of Allah on those who took usury, those who paid it, those who recorded it, and those who refused to give sadaqah.  

Your Question: In pakistan citi bank is offering cars(installments) with 6.99%.  I want to know if this is halal or Haram and in both cases please give some details to understand Islamic businees concepts.

In light of the above verses of the Glorious Quran and the hadith of the Prophet (saws), it is absolutely evident that both, the taking and giving of ‘riba’ is absolutely forbidden and declared haraam in Islam.  Buying a car from a conventional interest-based bank would be an illegal and haraam transaction in the sight of Allah Subhanah.