Question

how can potential resource can be actual resource

Answer 1

On the basis of their development and use resources 
can be classified into two groups, ACTUAL resources and POTENTIAL resources. 
Actual resources are those resources whose quantity is known. These resources are being used in the present. The rich deposits of coal in Ruhr region of Germany and petroleum in the West Asia, the dark soils of the Deccan plateau in India are all actual resources. 
Potential resources are those whose entire quantity may not be known and these are not being used at present. These resources could be used in the future. The level of technology we have at present may not be advanced enough to easily utilise these resources. The uranium found in India is an example of potential resource that could be used in the future. High speed winds were a potential resource two hundred years ago. Today they are an actual resource and wind farms generate energy using windmills like in Netherlands. 

EXTRA INFO 
Based on their origin, resources can be abiotic or biotic. Abiotic resources are non-living while biotic resources are living. Soils, rocks and minerals are abiotic but plants and animals are biotic resources.Natural resources can be broadly categorised into renewable and non-renewable resources.Renewable resources are those which get renewed or replenished quickly. Some of these are unlimited and are 
not affected by human activities, such as solar and wind energy. Yet careless use of certain renewable resources like water, soil and forest can affect their stock. Water seems to be an unlimited renewable resource. But shortage and drying up of natural water sources is a major problem in many parts of the world today.Non-renewable resources are those which have a 
limited stock. Once the stocks are exhausted it may take thousands of years to be renewed or replenished. Since this period is much more than human life spans, such resources are considered non-renewable. Coal, petroleum and natural gas are some examples.On the basis of their distribution resources can be ubiquitous or localised. Resources that are found 
everywhere like the air we breathe, are ubiquitous. But those which are found only in certain places are localised, like copper and iron ore.The distribution of natural resources depends upon number of physical factors like terrain, climate and altitude. The distribution of resources is unequal because these factors differ so much over the earth.

Answer 2

The potential resources are the resources that are unearthed in a region but cannot be utilized in present but in future. The two most important factors that are crucial for converting the potential resources into actual resources are "Time and Technology". For instance, Nagercoil's wind power. It remained a potential resource but during the course of time and technological advancement, it became an actual resource.