An employment advert is written to advertise a job vacancy. In most cases it is not written by the employer. In most cases corporate companies use of agencies to shortlist and source suitable candidates.
A well written employment advert should supply you with the following information:
Heading: attention grabbing - telling you the job title.
Information: the next section will cover the aspects of the position (where the position is, what it is paying and whether it has perks or not).
Detail: this is usually a summary of skill needed. More recently people have been putting duties in these sections - trying to show the person what it is they will be doing and/or what experience they need to get the job done.
Attention: information on how to will always be included in the adverts.
You, as the prospective employee:
Must want to do the job at hand.
Must fall within the advertised salary bracket.
Must have all the required experience as well as the desired qualifications.
Will have to follow the instruction given by the agent/ employer on submission of your CV to qualify for the position.