بِ is used
In the first sentence to mean that you feel -of- cold.. so you put it before the something that you feel of..
In the second sentence to mean the same of the first, because it means that you're welcome -of -your entering.. so the suffix بِ used to express what are you doing with the verb..
also the same in the last sentence, it means in question - do you enjoy the film - or - have you felt enjoyed -of- this film - you can even translate as - I used the film to enjoy -
كتبت بالقلم it means that you used the pen to write
لعبت بالكرة it means that you used the ball to play
سافرت بالقطار I traveled by the train - I used the train to travel -