Mulching is nothing but covering the soil around the plants with dried leaves/grass or coco peat. Such a covering stops water from getting evaporated and helps to retain moisture in the soil. Mulching is very beneficial in the winter and summer season.
After sometime the leaves start decaying and get converted into compost. This improves the fertility and health of soil.
Mulching also reduces the weed growth around the plants thereby saving all the nutrients in the soil just for the plant.
Mulching is ideal for slightly bigger plants. You can also mulch the soil around bigger plants by planting smaller plants around them. This may not add to the fertility of soil but it definitely help to retain the moisture in the soil and reduce the weed growth.