If it is important to your faith, someone else's faith, or that person, you can discuss it with them on a case-by-case basis and research or consult others on specific questions if you are not sure about them.
However, if the person who is saying this does not have a solid grasp of the Arabic language and is relying on translations or anti-Islam websites, their views about what the Qur'an says are likely to be flawed.
There is an enormous amount of material about the Qur'an online, possibly you will find many online resources about the issues they are bringing up.
At the end of the day, everyone has their own opinion on things. Someone who wishes to find fault in something will find fault in it no matter how even if they have to use their imagination. So if someone is extremely biased and just taking potshots, it might be better to leave the matter and only look into things that pertain to your own faith or understanding.
While the lack of contradictions in the Qur'an is part of its miraculous nature and a "proof" for it, at the end of the day, what is most important is the message of the Qur'an (divine unity, ethics, the nature of this life and the next, divine guidance, etc). This is what uplifts human beings..
The human being has the inner capacity to recognize the truth. If that message works for someone then debates over whether or not there are contradictions in the Qur'an are a secondary matter. However if someone absolutely rejects that message, or is not open to it at all, then proving that there are no contradictions/errors in the Qur'an will not make them a person of faith.