Question

please explain it from this figure​

Answer 1

Any process like Cliff erosion, a volcanic eruption, etc on earth's surface and bringing changes on it (earth's surface) , is known as external process.

Now, changes like weathering where the natural agents of weathering(i.e wind, water, glacier, etc.) breakdown and loosen the surface minerals and other rock particles, are transported away with them(agents of weathering).
☆ In u'r text book hey r telling that due to weathering the minerals and other rock particles are taken away (lowers the level of land) and when it is transported and deposited on other place (raise the level of land).
☆ And that Gradation is the process of levelling the land by means of moving agents like rivers, winds, sea and waves.