This section should be just a few lines introducing yourself, stating the purpose (to apply for the job) and revealing where you found the advertisement. If you are familiar with it-pathways.com you will know that I am personally not big on catchy one liners. But if there was ever a good spot for one - the introduction is the spot.
In the next paragraph describe your background as it relates to the job. But beware, don't lose focus on the prize. Ensure that you keep your background relevant to the offered job. If possible list similar experiences and any high level achievements. There's no need to enter into a great deal of detail at this point. Your resume and interview will cover the experience behind the achievement. It is important, however, to establish a connection between yourself and the recruiter. Don't assume that the employer knows why you are qualified for the job. Spell it out in a manner that clearly relates back to the skills listed in the advertised job.
If you don't have much (or any) work experience to speak of consider how you attained the skills required for the job. Studies? Hobbies? Interests? Clubs and memberships? Literature? Even at an entry level, Information Technology candidates should have some background in the field. Look at some of our articles to give you ideas.
List key points in your training or experience that demonstrates why you meet the criteria.
Once you have established a relevant background address the immediate requirements listed in the job advertisement. Once again, don't enter into too much detail. Simply state why you can meet the criteria. Include any achievements, relevant certifications or awards that may strengthen your argument. This section should be very convincing. Not only are you trying to show that you are suitable for the position, but you are also trying to show that you are the most suitable for the position. If you have several sources of training or experience for the one skill, list them all so that the employer can see the depth of your experience. Don't leave anything to the imagination. The more sources of knowledge and experience the better.
Conclude with departure formalities (thank you for your time etc.) as well as a 'call to action' such as an interview request.
Just like the introduction, keep this section concise. I try to keep this section friendly and positive such as 'I would welcome the opportunity to present myself at an interview'. I tend to avoid more direct assertions such as 'I will call you on Friday to arrange an interview' or statements to that effect. This approach has worked for me over many years. My thoughts are that the employer is more than capable of picking up the phone to contact his preferred candidates so forcing his hand may seem impertinent. This may be a regional quirk however, perhaps in some parts of the world this proactive approach is an accepted practice.
See Cover Letter Examples here.