Replying to International travelers, i need advice and help

alright. so i just booked my flight into dublin, ireland.

I need to know whats up. i've heard you need a visa for some countries? or will just a passport work for short visits?

what to get if i want a cell phone? how to get around the best way? bus? train? cheap flights over to europe?

social things i should know?

anything and everything will help. i'm planning on going from ireland, to england, to france, to germany. and if i have enough time, to prague.

+k to and serious and helpful answers.