Hijab literally means 'to cover'.
In Islamic Shari'ah (Law) the word Hijab means covering a woman's body.
It is an undeniable biological fact that both men and women are attracted towards each other by their physical appearances. Islam is fully aware of this human weakness and as a result, it has laid down certain guidelines, which if followed carefully, may create a healthy society where crimes against women can easily be checked.

"And tell the believing women to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts) and not to show off their adornment except only that which is apparent (like both eyes for necessity to see the way, or outer palms of hands or one eye or dress like veil, gloves, head-cover, apron etc.), and to draw their veils all over their Juyubihinna (i.e. their bodies, faces, necks and bosoms) and not to reveal their adornment except to their husbands, or their fathers or their husband's fathers, or their husband's sons, or their brothers or their brother's sons or their sister's sons, or their (Muslim) women (i.e. their sisters in Islam), or the female slaves whom their right hands possess, or old male servants who lack vigor, or small children who have no sense of feminine sex. And let them not stamp their feet so as to reveal what they hide of their adornment. And all of you beg Allah to forgive you all, O believers, that you may be successful." Surah (Chapter) An-Nur (The Light) The Qur-an 24:31

At another place the Qur-an specifically tells the women to cover their entire body
when they go out for any work:

"O Prophet! Tell your wives and your daughters and the women of the believers to draw their cloaks (veils) all over their bodies. That will be better, that they should be known (as free respectable women) so as not to be annoyed. And Allah is Ever Oft-Forgiving, Most Merciful." Surah (Chapter) Al-Ahzab (The Confederates) The Qur-an 33:59

Islam advocated decency in dress.

O you Children of Adam! We have bestowed on you raiment to cover your shame as well as to be an adornment to you. But the raiment of righteousness, that is the best. Such are among the Signs of Allah, that they may receive admonition. Surah (Chapter) Al-A'raf (The Heights) The Qur-an 7:26

Moreover, Hijab is an attitude, and is neither a sign of backwardness nor submission to men. Wearing the Hijab isn't just a matter of simply putting a piece of cloth on your head, is a way of thinking and behaving, and accepting yourself for who and what you are.
Basically it constitutes an Islamic way of life, it is a statement which indeed should portray a certain attitude.
A woman may wear a long skirt and a scarf, but if she flirts, then she can't be really described as wearing the Hijab.

Clothes for Muslim women should be long, loose and not see through, after which any style of clothing is applicable. The whole idea involves conducting oneself with dignity at all times.

As mentioned earlier, the Hijab depicts a statement, and that is something one should be continually aware of. It identifies one as a Muslim. With Hijab comes a big responsibility. People will judge Islam through the person wearing Hijab.

Wearing the Hijab, is an automatic means of Da'wah (Invitation). Curiosity prompts people to ask question, generating opportunities to show the non-Muslims the beauty of Islam. A Muslimah may get strange stares at times, but amazingly most people are sincerely interested.

Hijab does not restrict a Muslimah from doing the kind of lawful things one wants to do. it is a blessing because it keeps acheck our behaviour continuously, preventing us from doing the things that Muslims shouldn't be doing anyway. Anything (with the blessings of the Almighty, is possible) -studying, working etc. etc. -provided it is within the bounds of Islam (Halal).

Sometimes, however the decision to wear the Hijab can become extra complicated through external pressures, notably family and friends. Unfortunately, even some Muslims nowadays look upon the Hijab as being too extreme, and the like and when these attitudes come from members of your family then the decision becomes all the more difficult.

It is to be done for Allah (God), and he will make it easy for you, by softening the hearts of those that may not be all that encouraging. Eventually they themselves will want to follow you because deep down they know that it is the right thing to do.

If that doesn't help, then this should convince you: On the authority of Abu Hurayrah (R) who said that the Messenger Muhammad (S) said : Allah the Almighty says: " I am as my servant thinks I am...If he draws near to Me a hand's span, I draw near to him an arms length; and if he draws near to Me an arm's length, I draw near to him a fathom's length. And if he comes walking, I go to him at speed."

On the other side, it is important to ascertain the motive for wearing the Hijab. If one is wearing it to please one's husband, to impress people at the mosque, or just as a change, then please think again. Hijab (as with everything else) is to please Allah (God) only, any other motive will not sustain that conviction.

Hijab is not only a woman's issue. Muslim men have to follow a dress code too, no matter if it isn't as extensive as for women it still exists! The men,like women, should also wear loose clothes. Their attitude to all women should also always remain respectful, as the women's attitude to men should be.

"Say to the believing men That they should lower Their gaze and guard Their modesty: that will make For greater purity for them: And Allah is well acquainted With all that they do. And say to the believing women That they should lower Their gaze and guard Their modesty: that they Should not display their Beauty and ornaments except What (ordinarily) appear Thereof; that they should Draw their veils over Their bosoms and not display Their beauty except To their husbands, their fathers, Their Husband's fathers, their sons, Their brothers or their brothers' sons, Or their sisters' sons, Or their women, or their slaves Whom their right hands Possess, or male attendants Free of sexual desires. Or small children who Have no carnal knowledge of women; And that they Should not strike their feet In order to draw attention To their hidden ornaments. And O ye Believers! Turn ye all together Towards Allah in repentance that ye may be successful." Surah (Chapter) An-Nur (The Light) The Qur-an 24:30-31