In my landscaping i mean ( in mulch) there is light yello or you can say light skin color fungus is growing.
what is that? what are the reasons? how can i get rid of?
Fungus is often a normal component of soil and doesn't need removal. If you don't like how it looks, loosely rake the area. More info on fungus in mulch here: https://www.gardeningknowhow.com/garden-how-to/mulch/common-mulch-fungus.htm