According to the Copyright update in 1978 and every one after that, as soon as you put down a copy of a work, whether written, filmed or recorded (hard copy or purely electronic) you are copyrighted. You can register that copyright directly with the US copyright office. You do not have to go thru a company like ASCAP or BMI etc. Go to the website and read up on it.
BTW - CCLI also will register your songs just like those other companies (for a fee of course).
This is true, but creates a problem should you ever have to go to court to defend your ownership. Unless you can provide undeniable proof of ownership, the courts usually side with the party who has a valid copyright registration from the Registrar of Copyrights. The "poor mans copyright", as it's known, has never been a great idea. It was based on a loophole that has been further muddied with newer copyright legislation in the digital age.
When in music school I took some music law classes (copyright, publishing, contracts, licenses, et al) and the advice given by lawyers is to properly register each work with the Registrar of Copyrights in Washington DC and to then register them with a Performing Rights Organization (PRO) like ASCAP, BMI, SESAC if the work will be performed live or in recorded form.
As far as self-publishing. I do that as a registered BMI songwriter. BMI automatically assigns self-publishing rights to all their registered songwriters. This is not the case with ASCAP. ASCAP requires that you assign publishing rights to a registered publisher. Of course, you can register with ASCAP as a songwriter & as a publisher to get around this.
Hope that helps
I am registered with SESAC but CCLI has worked the best for me.