What is Tajweed?
Tajweed means to recite every letter correctly, i.e. from its proper origin of pronunciation coupled with its stipulated attributes.
Allah Ta'ala says in the noble Qur'an, "And recite the Qur'an with Tarteel (in a slow pleasant tone and style)." (73:4)
The Prophet Muhammad (Sallallaahu Alayhi Wasallam) has said, 'Indeed Allah desires that the Qur'an be recited in the manner it was revealed.'
When asked about the meaning of Tarteel, Ali (Radhiallaahu Anhu) replied, 'It means that the Qur'an should be recited with Tajweed and with due observance to the rules of Waqf (pausing or stopping at the end of the verse).'
Necessity of Learning Tajweed:
Since the Qur'an emphatically commands us to recite the Qur'an with Tarteel, we have to recite it with Tajweed. Tajweed is not like all other subjects which we are able to separate from the Qur'an but instead Tajweed and Qur'an work hand in hand.
According to some scholars, the verse, 'Verily my people have renounced the Qur'an' (25:30) has two interpretations. Firstly, it could mean that they had renounced the Qur'an by not believing in it and practicing upon it. And secondly, it could mean that they used to recite the Qur'an in such a disgusting manner that it sounded like senseless and meaningless jabbering.' Reading the Qur'an without Tajweed could also be included in the second interpretation.
The Prophet (Sallallaahu Alayhi Wasallam) has said, 'The Qur'an will either testify in your favour or against you.' Hence, if we fail to observe the requirements of the noble Qur'an during our recitation, the Qur'an will testify against us. If we are unacquainted with these prerequisites, we are compelled to acquire the laws of Tajweed.
Due to the vastness of the Arabic language, any small mistake in pronunciation of a letter or word may change the meaning of that word. For example, the word 'Qalb' (with q) means heart, if read 'Kalb' (with k), it will mean a dog'.
So just as how in any other language we learn pronunciation of letters and words, for example, in English we learn that 'ph' stands for 'f' (as in phone) and not pone. Similarly, in the Arabic language, we also have to learn pronunciation of letters and words, which we term as 'Tajweed'.
Some people read so much of the Qur'an but because they do not know the correct pronunciation of the letters, they change the letters, which then changes the words which eventually leads to the changing of the sentence and meaning of the Qur'an.
We should remember that from the time and generation of the Prophet (Sallallaahu Alayhi Wasallam) till now, no one has ever denied this fact that Tajweed is definitely important. It is only now in our generation that people have lost respect and forgotten the status of Tajweed.
We get some people nowadays who spend hours and hours reciting the Qur'an thinking that they are getting and attaining great rewards. But because their pronunciation of letters is incorrect, a very big problem arises. It sounds very small when we say, 'I am only pronouncing a letter incorrectly.' But did this thought ever cross our minds that when a letter changes in a word, the word changes and if a word changes in a sentence then the whole sentence changes and eventually the meaning also changes.
The Qur'an is the word of Allah. If we change the word of Allah then Allah Ta'ala will definitely get angry with us and take us to task. So from all this, we can see the importance of reading the Qur'an with Tajweed.
May Allah give us the ability to read the Qur'an correctly so that we may earn the mercy of Allah Ta'ala.
Source:
http://www.islamicweb.net
Here's some links that may be useful:
www.abouttajweed.com
www.reciter.org
However there is no substitute to learning from a qualified teacher.