To get around in Berlin you can use public transport provided by the BVG. Please find a link to their website (English) here. For most of your purposes a ticket covering the inner city (Berlin AB) should suffice.
Tickets and Fares (Berlin AB)
A Single Ticket for 2,10€ is valid for two hours (no return or round trip).
Day Passes for 6,10€ are valid for as many journeys as you like until 3:00 a.m. on the following day.
4-Trip Tickets consisting of four single tickets are 8,00€.
The Welcome Card is an offer for tourists that includes a discount of up to 50% on more than 130 sights. It comes with a guide and map and is available for 2, 3, or 5 days costing 16,90€, 22,90€, and 29,90€ respectively.
The Berlin Welcome Card tickets are available at all ticket vending machines (without guide). The guide can then be collected from various outlets on presenting the ticket.
The BVG is also offering Group Tickets for up to 5 people which are valid until 3:00 a.m. on the following day. They cost 15,90€.
Please note that the vending machines don't take notes bigger than 10 Euro.
From Wednesday on we're expecting temperatures from 2°C up to 7°C during daytime. We're also expecting sleet or drizzle. Bring solid shoes!