In some plants, one of the Synergids starts to die. It must release some chemotactic agent because the pollen tube is attracted to it.

The Pollen Tube grows through the Micropyle & may enter the senescent synergid. The pollen tube wall degrades and the sperm are released.

The Egg and the Central Cell have incomplete cell walls & the sperm has no wall. One Sperm enters the Egg while the other enters the Central Cell.

The Zygote is formed when a Sperm nucleus fuses with the egg nucleus (Syngamy). This will develop into the Diploid Embryo.

The Endosperm is formed by the fusion of a sperm nucleus with the nuclei of the Central Cell. It is therefore Polyploid (3N). The Endosperm surrounds the developing embryo and provides a source of nutrition for the Embryo during its differentiation & during Germination of many plants.

Both   have a Suspensor. Dicots have a suspensor that is a unicellular filament, while Monocots have suspensors which are several cells in width.

In both cases, the suspensor is minute compared to the Embryo.

In some plants, like coconut palm the embryo is very small and is surrounded with a large Endosperm. Coconut Milk is liquid endosperm and the "meat" is solid endosperm. The endosperm is used during seed germination in the latter case.

In other plants the Endosperm becomes completely cellular early in development and may be consumed by the embryo. Nutrients absorbed by such embryos are stored in their Cotyledons.

Early stage in Lily Embryogenesis. note the Nuclei in the periphery of the Endosperm. Cellularization has started but most of the Endosperm is liquid.

Lily Embryo Showing the Suspensor.