So when asking questions, its usually good to follow these rules:
1) What have I tried?
2) What do I expect it to do?
3) What does it do?
so for 1) you mention <br/> but not how you use it, nor do you mention what your template looks like.
2) Other than "Expect it to work" i don't really know what you are expecting,
3) No idea (does the <br/> show up in view source?)
I'm guessing you are using a variable and outputting the variable with a new line. By default jelly will now escape any html in variables to prevent security issues. So if you are adding <br /> inside a variable, it'll probably not work.
IF you are just wanting newlines to work, you could wrap your content in a PRE tag, and then newlines should work.
But generally you shouldn't have formatting in your variables.
If i made the wrong guess and you are trying something else, then I need 1,2,3 answered again.