if it wasn't for the movie "in bruges" starring collin farrell, this place wouldn't be as touristic and famous as it is now. so watch the trailer or better the movie to get a very great first impression of bruges.
since it is only an one hour trainride from brussels and also very inexpensive you can just go there for an afternoon and take a walk through the beautiful historic city center. you can either get a ticket right at the trainstation or you buy your ticket online if you prefer that.
the city center is in a few minutes walking distance from the trainstation in bruges. you basically have maps all over the city that shows you the main and the most interesting buildings. after a 2-3 hours walk you have seen it all and you could go for a canal cruise or just for a coffee and chill. they say that bruges is the venice of the north so i guess a tour on a boat would be great even though i did not go for it because it was raining. i rather sat down for a coffee and just observed the people and tried to absorb as much as possible of the place.
if you are not much of a walker then you should go for one of there horse drawn carriage tour. i just thought it was pretty expensive: 30-40€ for 30 minutes. and also it is hard to understand the driver talking about the history of the buildings because of the noise and your pictures will also turn out very wobbly.
insider tipp: try not to go there during summer. i went there in march and it was already pretty packed. so i don't want to imagine what it would be like in summer.