Ecological succession refers to

Ecological succession is the slow, orderly way the living things in an area change over time until the community becomes stable. Because the steps follow a known pattern, scientists can predict what will come next.

It starts with pioneer species — simple organisms like lichens and mosses on bare rock, or fast-growing weeds on cleared land. They break down the surface and add humus, making soil. Grasses move in, then shrubs, then trees, and each new group changes conditions for the next. The final stable stage is called the climax community, such as a mature rainforest.

The other ideas are different topics: organisms moving from one habitat to another is migration; natural selection is how evolution picks favourable traits; and species fighting over limited resources is competition. Competition does happen during succession, but it is not what succession means.