ASCAPand BMI or SESAC are services that collect royalties for songwriters. They are actually called Performing Rights Associations.

ASCAP costs a small yearly fee of $25 for writers and $50 for publishers. BMI is free to songwriters and an upfront $100 fee for publisher membership.

You may only be a member of one association. BMI is suggested for blues, r&b, soul, and country music writers and performers (there is a bit of history behind that reason but I will not get into that here). To become a member of either organization you have to have sold (at least a small amount I believe if memory serves me correctly sales to friends and family count if you make a receipt) of albums or songs to be eligible but you can be a charter member of ASCAP for up to 3 years before you must sell any albums or songs to become eligible for full membership.

Both organizations can help further a songwriters career, and to receive royalties you must be a member of one of them. There are many other performing rights organizations like these in many countries. These 2 are the recommended for the United States. There are links on my link page to both ASCAP and BMI web sites, you can find more information on those sites about their services.