For people who missed the previous weekend passes you get another chance:
Originally Posted by SWTOR
This weekend, BioWare and LucasArts will be holding another Weekend Pass Free Trial, allowing people who are curious about Star Wars™: The Old Republic™ the opportunity to begin their own personal Star Wars™ saga free* of charge! This Weekend Pass Free Trial will begin on Thursday, April 19th at 12:01AM CDT / 5:01AM GDT and run until Monday, April 23rd at 2:00AM CDT / 7:00AM GDT.
Quick FAQ's about the pass:
- There is no payment or credit card required.
- You can play for up to four full days free of charge.
- Your trial characters will be saved to your account, so you can continue on your Star Wars™ journey upon purchase of the game and redemption
- You will be able to experience the first fifteen (15) levels of the game, exploring the Origin Worlds of each character class, and potentially visiting your faction’s Capital World.
- You will also be able to take part in Player-vs-Player Warzones, or join up with friends to battle through one of the many Flashpoints in the game.
- Only people who have not participated in any other free trial can take part in the weekend pass.
(Source)