how do I balance equations such as this one... magnesium bromide+chlorine

Hello Roxy!
Well : this seems to be your homework, so why don't you start posting here the proper chemical formula for magnesium bromide and chlorine first? Once you do we'll take it from there!

1) Write down the formulas for each of the compounds or elements.

2) Add multiples of each compound on the left side of the equation to get them to add up correctly on the right. For example, let's say you're balancing

H2 + O2 = H2O

You have two hydrogen atoms on the left and two on the right. That appears to be balanced. However, you have 2 oxygen atoms on the left but only one on the right. So you can do this:

H2 + 1/2 O2 = H2O

If you're wanting whole numbers (who doesn't), simply multiply by a common denominator -- 2 in this case.

2 H2 + O2 = 2 H2O

Hello Roxy

Have not heard from you yet... why?

As to balancing chemical equations : have a look here on an article of chemical valancy. (http://en.wikipedia.org/wiki/Valence_(chemistry))

Have a look at chapter 'Valences of the elements' (colored periodic table with data on all elements)
Here is your starting point. Write down the valency of each atom in the magnesium bromide+chlorine mixture.