i want to travel from porto portugal to alicante spain by train how can i find out about this?

There are no direct trains from Porto to Alicante. You can use the Deutsche Bahn (German railways) journey planner at http://reiseauskunft.bahn.de/bin/query.exe/en to see some suggested routes for the specific time and date you wish to travel, though you will not be able to purchase a ticket online for this journey from Deutsche Bahn.

The quickest journey leaves Porto at 17:55, changes in Porrino and Madrid, arriving in Alicante at 12:45 the next day, a total travel time of just under 18 hours.

Neither CP (Portuguese rail) nor Renfe (Spanish rail) has a thorough international journey planner on its website, but either should be able to sell you a ticket. I'd recommend calling CP, as the best prices are often found by calling the country in which your journey starts. Their number is +351-21-854-5212.

Good luck, and enjoy your trip!

- Take the 15:47 air-conditioned Alfa Pendular tilting train from Porto (Campanhã) arriving at Coimbra B at 16:44. Seat reservation required.
http://homepage.mac.com/wkaemena/FS/Portugal/Porto/AlfaPendular1/

-The Sud Express leaves Coimbra B at 18:26 overnight to various destinations in Spain.
You can book this at http://raileurope.eu/

-Once in Spain, book tickets onward to your final destination at http://www.renfe.es/ .