One-way ticket for the public transport is 30 CZK (30 min) or 40 CZK (90 min). You can buy a permanent ticket for the public transport valid for one month for 550 CZK (~20 Euro).
Fares: http://www.dpp.cz/en/fares-in-prague/
Prague Public transport trip planner: https://www.dpp.cz/en
The organizers recommend using an app (such as litacka) on mobile phones. Single usage and monthly tickets can then be bought easily.
Printed tickets can be bought in yellow vending machines
Remember to validate your ticket when entering the metro, bus, or tram. Validation is required only once at the start of your journey, so there's no need to re-validate when making connections.
Three metro lines in Prague
Střížkov is the station of the DUO congress cente
Muzeum, Můstek, Staroměstská are very center
