According to their official site, "PlayStation Plus delivers a whole new level of access and convenience so you can spend more time doing what you love... playing games! PlayStation Plus includes cool stuff like Full Game Trial where you can try before you buy. Or, have the opportunity to get early access or invitations to select demos and betas. Best of all, the value pays off with killer exclusive discounts and free games and content from PlayStation Store."
You may be asking yourself, "What's this going to cost me?" They actually offer a couple of different pricing options, and it's not as expensive as you might thing.
1 year - $49.99
3 months - $17.99
Right now they're running a special promotion for 1 year memberships. Purchase a 1 year subscription and you get an extra three months for free (that's about $3.33 per month).
Visit the official Playstation Plus site to learn more.