These are your staring pieces. Pls know that I have not tried hard to be perfect here, on an actual garment the welt would be much neater and nicer. My purpose was only to illustrate the technique.
Pocket facing sewn to pocketing at serged edge and basted at other long edge
Pant front - pocket is marked.
Place pocketing facing down. Position pant front on top of pocketing. Note: the facing should be face down and to the side opposite to the outseam.
Position welt piece on top of front - WS out
Stitch
Cut
Form welts
Stitch the triangle
Baste or tape over the top edge of the welt
This is what you have on the inside
Understitch 1/16" from the edge.
Stitch the serged edge of the welt to the pocketing
Fold the pocketing.
Lift the front
Understitch 1/16" from the edge
This is what you have between the welt and the outseam
Trim (preferably by pinking) about 3/8" from the facing edge
Serge the lower edge of the pocketing
Baste the waist and the outseam catching all layers.
Trim away at the waist the excess of the welt pieces
And we have a pocket...
Yep...
You can even put your hand inside!