A resource is anything that is useful to people. Natural resources can be divided into renewable and non-renewable resources.
A renewable resource can be used again and again, so is more sustainable, eg water, wind, wood, sun and wave energy.
A non-renewable resource will eventually run out, so it is not sustainable in the long run, eg fossil fuels such as gas, oil and coal. There is only a finite supply of non-renewable resources.
All resources, both non-renewable and renewable, need to be carefully managed. For example, you can use a non-renewable resource in a way that helps to lengthen its use, eg re-using old tyres in road building materials. Some renewable resources may become polluted or overused by man.
Most of the Earth's energy comes from the Sun, and this energy can be used in a direct way, through solar power. Energy in other materials could be said to have come from the Sun indirectly, eg coal and oil are formed from dead plant and animal life. Both coal and oil take thousands of years to form, and therefore cannot be replenished in a lifetime.