Steps in Making an Origami Envelope with a Leaf

Material: A rectangular sheet of paper.
Step1: Now here is a non-square rectangle. Let's put the long sides vertically. It would be denoted as \(▭ABCD\). The two vertices above are A and B, while the ones below are D and C.

Step2: Place the vertice A onto the line BC and let the fold 1 pass the vertice B.(Fold it inside!)(It means the fold 1 places the line AB onto BC here.)(In this circumstance there's a unique fold.) Now we get a right triangle. Let's call the point where now the vertice A lands A' and the point where the fold 1 and the line AD intersects E.

Step3: Place the vertice D onto the line EA' and let the fold 2 pass the point E.(Fold it inside!)(It means the fold 2 places the line DE onto EA' here.)(In this circumstance there's a unique fold.) Now we get a new right triangle. Let's call the point where now the vertice D lands D' and the point where the fold 2 and the line DC intersects F.

Step4: Place the point E onto the line EA' and the fold 3 is the line FD'.(Fold it inside!) Let's call the point where now the point E lands E' and the point where the fold 3 and the line BE intersects G.

Step5: Place the line BE onto GE' and the fold 4 is perpendicular to the line BC.(Fold it down!)

Step6: Unfold the folds 4,3,1 and flip the paper around horizontally. Now you can see a squared falling diagnol slash 5. Now the vertice in the bottom right hand corner is B and the one in the upper left hand corner is G.

Step7: Place the vertice B onto G. (Fold it inside!)Let's call the fold 6 and the point where B lands B'.

Step8: Place the point B' onto the fold 6 and the new fold 7 is perpendicular to the slash 5.(Fold it outside!)

Step9: Place the fold 7 onto 6.(Fold it inside!) We get a new fold 8.

Step10: Place the fold 8 onto 6.(Fold it inside!) We get a new fold 9.

Step11: Unfold the folds 9,8,7. Fold 7 folds just like you are making a fan.

Step12: Flip the paper around horizontally.
Step13: Fold along the fold 3 and let the point E land on the line EA'.
Step14: Fold along the fold 1 and let the fold 4 land on the fold 1.

Step15: Fold along the slash 5 and let the vertice A land on the line BC.(Fold it inside!)

Step16: Fold along the line EB' and let the vertice C land on the line BC.(Fold it up!) Let's call the line where CF lands C'F'.

Step17: Fold along the line C'F' (Fold it down!) and twist along the fold 6.

Ta-da! The envelope is done.