Examine CDs put out by some of the artists who perform the types of songs you compose. You will often find management information for the artist on the cover of the CD. You can also find the artist's music publishers and record company. All of these bits of information can be used to submit your own songs for consideration. When using this information without submission guidelines, it's best to write a brief query letter that introduces who you are, states that you have a song for (specific artist) to consider, and ends with a polite "thank you for considering my work." Ensure that your contact information is on the letter as well as on the CD recording of the demo you send. Include a songwriting bio and resume if you have other credits. This is considered submitting blind and is the least effective method, but it can work.
Purchase a copy of the "Songwriter's Market" or consult a database of record companies, music publishers, and music producers (see resources). These resources are essential for submitting your songs to the right people and getting them listened to. The "Songwriter's Market" contains complete contact information for markets looking for songs to purchase. It tells you how to submit your material. Submitting material to one of these markets and following the guidelines can help ensure your work is being looked at.
Determine whether or not you need an agent. This is a personal choice. Some record companies and producers won't listen to material not delivered by an agent, but there are many that will. An agent will take a portion of the royalties you make from a song. If you are just starting out, consider going it alone for a while. You can always consider an agent when you begin to get heavy interest in your work.