Theres many ways to make a burn transition, altho it depends on what type of "burn" you want.
The easiest way is the Burn Film effect in After Effects. You can also achieve that same effect by scaling up a bunch of randomized feathered white circle masks/ellipses over a black background and using those as mattes etc.(particles will work too). Setting an orange-yellow solid to Add at maybe around 6% or so opacity may help give it a nicer orangey tone to your gradients(if you desire).
And of course for a more advanced fiery burn away there are a lot of tuts you can find for different tips to achieve that tho it will be a little complicated for a beginner, especially if you really want to sell the detail. But you won't learn unless you push yourself, right?!