When wearing something tighter, shorter or trousers, having a bit of a bulge in the lower area can reduce the feminine look you are trying to achieve. Nothing is worse than seeing a woman in a beautiful dress with an unsightly bulge swinging about.
Tucking the penis and testicles away helps with achieving a more feminine shape. The idea here is that you push the testicles back into the sack they descended from when you hit puberty. This may be a bit uncomfortable to start with.
Of course if you are taking feminising hormones, your testicles will have shrunk anyway, making it a bit easier. After pushing the testicles back into your abdomen, you then tuck the penis back in between your legs.
The other less complicated method some cross dressers use involves big knickers or control pants. These are the pants genetic women use to hide larger stomachs and they can be very useful in holding things in place discreetly for you. Some t-girls like to couple these with some control-top tights.
Some other pants that are specially designed for cross dressers are called gaffs. These can be found on many specialist clothing websites. They have a restructured crotch that smooths down your front to create a smooth, feminine look.
Using tape can also help with tucking the masculine bulge between your legs, but you need to beware of using one with too much adhesive unless you have either waxed or would like to!
TIP:
Control pants, tucking and gaffs can all help give you a smoother look.