Fold your square across the diagonals.

Now fold the bottom half upwards so you get a triangle.

Fold the two corners down along the vertical, centre crease.

Again, using the same corners, fold them back up to form triangles. Make sure the top of the triangles are level with each other.

Right, if you grab the top spike you will find there's actaulyl another one inside so..

... pull it right out...

...and flatten. Voila, this is what you should have.

Flip it over.

Right this is the tricky step so I've marked on the creases you will be making.
Note the triangle is shape 1 and the spike bits are shape 2.

Mountain fold the triangle (shape 1) so it's creased towards you...

..whilst folding the two spkies (shape 2) together. The shape should flatten but the spike behind (remember how there was one in the other) might not invert itself so give it a hand.

This is the shape you should get when it's flattened. It's cool if you don't get it the same way I've explained. End result counts :)

Fold upward the top flap. This will be one wing. Whilst folding...

...fold in the left point and flatten so it forms a triangle. What you have just folded is a wing.

It should end up like this. Now you can fold the other wing behind...

...like this. Looking like a bird yet?

This is what you have so far. The left spike is the neck of your bird and then you have your wings and a tail sticking out at the top.

Reverse fold the neck. So open up the neck and fold it part way down...

... and press the neck together. Ta-daa! A beak.

Finally, fold the bottom of your bird into a triangle to form a base. This will allow the bird to stand up and 'nest'. Do this on both sides.

Behold... a bird.
:D