why is it important to weed and fertilize the ground

Fertilizing is undertaken to replace the nutrients in the soil that the plants used in the previous year(s). Plants need nutrients to remain healthy.

Weeds are basically unwanted plants. They may look ugly, cause damage to property or cause allergic reactions. They also use the nutrients you have supplied for your wanted plants, block out their light or even strangle your plants to death.

Thats it in a nutshell Rydeboyz.............

Amen

Can I just add two points for a different perspective:-

First, not all plants need the soil to be improved - if you are growing native wildflowers for instance, they won't like it and some garden plants actually flower better if they are in fairly poor ground. Adding fertilisers to soil can result in plants growing too quickly which makes them prone to wind damage and pests.

Second, if you leave an area of soil with nothing at all growing on it for too long damage can actually occur to the structure of the soil which will effect its aeration among other things, so in some circumstances a protective covering of weeds is preferable to growing nothing at all.