Here is information about getting to Cambridge. Local buses, taxis, and bicycle hires may be useful. If you are coming from elsewhere in Europe, the most convenient airport is Stansted, and taking the train is also a possibility.
If you arrived in Cambridge by train and are staying in Selwyn, then here is how to get from the rail station to Selwyn by foot and here is one way to do it by public transport. There is also a taxi rank at the station.
If you arrived in Cambridge by coach, then here is how to get to Selwyn.