Instead, it depends on pollination. Pollination refers to the process where the male gametophyte, in the form of pollen, travels to the female gametophyte, in the form of the seed. The pollen can travel over a much greater distance than sperm. This ability to disperse is important and reduces the requirement for water. In saying this, it must be noted that when the male part is in the form of sperm, it requires water. This is partly because the sperm does not have any vascular tissue. This is also because the sperm's only form of movement is swimming, which clearly requires water. For terrestrial plants then, not having water is a major problem. Having a seed and pollen solves this problem and makes dispersal without water possible. Pollination then occurs when a pollen grain reaches a seed and passes through its micropyle, a tiny hole in the seed covering...

The male and female parts then meet and a new plant is produced. Most importantly, there is no requirement for water for this process to occur, making terrestrial plant life feasible.
The other important point about the seed is that it protects the female gametophyte from difficult conditions. The embryo within the seed provides nourishment to the female gametophyte. The seed covering also protects the seed from any kind of harsh conditions, including heat, cold, or dry conditions. The seed is essentially able to lie dormant while remaining nourished and protected until conditions improve. This also allows for dispersal and also solves the problem of terrestrial life for plants.

Overall, this explains what a seed is, what its function is, and how it solves the problem of terrestrial life for plants.