First open a new document, 500 x 500 pixels with a black background,

then you type what you want to for example "I like pie" then rasterize the text layer,

then open up the Hue and saturation box, (ctrl u, or Open apple u) Click the Colorize box and then change the Hue to 38, and the Saturation to 60, then adjust the lightness until the words look orange.

Now duplicate the layer, go to the first layer and smudge it to how ever you like it and then go to the copyed layer.

On the copyed layer go to the blending options and choose Color Dodge or Color burn.

And thats it, you should have fire-like text.