I will like to visit malaysia and singapore but i have my return tickets from malasiya please guide me with?

visa norms.do i need to take double entry visa from malaysian embasy.and visa from singapore embasy too?what is the best mode of transport to go to singapore from malaysia.what is tenure by bus/train?can the tickets be booked before hand for train and bus?please let me know the website for the train/bus from malaysia to singapore.