I will be solo in Berlin between 15-20 Dec, 2016, it is my first time. I just want to know the city in a relaxed manner, walking around. I am interested in the Botanical Garden if there is one, I am not interested in shopping. Attending a clasical music concert would be OK. I guess movies are in German so I would not understand them. A couple of museums also. Any suggestion to stay in, like a BB place, not too fancy or expensive? Thanks for your comments.

There is a place called the Odeon (kino) that shows films in their original language, so you might actually be able to see something in English. It's near the Rathaus Schöneberg where Kennedy gave the "I am a jelly doughnut" speech.

Check out Ravenna Hotel in Steglitz. It's not a B&B but I think it's pretty reasonable, although you should be able to find good prices in the city.

The Reichstag offers an interesting tour that shows off the modern additions to the war-damaged house of government. The glass dome provides a vivid panorama over the city skyscape. For the tour you must make arrangements in advance; think of it as an advance reservation with security concerns.
https://visite.bundestag.de/BAPWeb/p...st.jsf?lang=en

If you want to see movies in English check out the listings at exberliner.com
Aside from the Odeon, many more movie theaters show films in original version (i.e. mostly English). One larger cineplex with OV movies only is the CineStar Original at Potsdamer Platz.

The Botanical Garden in SW Berlin is quite nice. And the greenhouses a good escape from the winter weather.
http://www.botanischer-garten-berlin.de/en

It's pretty hard to recommend any specific classical music concerts. You will find any kind from a free matinee in a church to a high-end performance at the Philharmonie.
It will be best to browse the city's TI website for upcoming events at visitberlin.de

The best thing you can do your first day in Berlin is to go on a good walking tour. This will give you an excellent orientation to the city, provide tips for other things to see and do, as well as tell you some fascinating history.
Recommend Insider Tours for the best and most interesting tour. For 14 euro for a 4 hour tour, you can't beat the price for a professional tour.