DEFINITION OF GEOLOGY
Geology is a science which studies the earth planet and exploit its natural resources (solid minerals, oil and gas and water) for man’s use and also to  predict and prevent where possible natural disasters (  landslide, earthquake, volcanoes etc.) and to investigate earth's history.
The above definition is a way of pointing the readers to the relevance of geology to human. We will keep this discussion as simple as possible as it will serve as guide to prospective student of geology. Some of the discipline in geology includes:
*Sedimentology
*Geophysics
*Hydrogeology
*Geochemistry
*Petroleum geology
*Engineering geology
*Economic geology
*Marine geology
*Micropaleontology
*Structural geology
The usual practice in universities is to introduce courses that will prepare you towards the above discipline. Consequently, first and second year student may not come across these courses until third year of study. However that is not a standard it is my own experience your region may not adopt same method.
For the purpose of introduction I will only write few lines on each of the discipline mentioned earlier. For further details check text.
Sedimentology: studies sediment (particles carried by wind, air, water) deposition and detail transformation of the sediment into different rock types after deposition.
Geophysics is used mostly, in exploring earth interior for natural resources and groundwater contamination/exploration with the help of some physics principles and equipment.
Hydrogeology is chiefly concern with the study of groundwater exploration and exploitation. .hydrogeology is employed in town planning (dump site location to avoid contamination of ground water), mine construction (to avoid the aquifer bed/unit to eliminate flooding in mine construction) and dam construction.
**Aquifer means water bearing rocks units/beds in the subsurface which can yield/give-up such water when drilled.  
Geochemistry is concern with the exploration of natural resources by using statistics and comparing the figures gotten within the overall area of interest. The area with the highest value indicates the possible accumulation of natural resources of the study area.
Petroleum geology studies the accumulation and exploitation of oil and gas using geochemistry, geophysics and some other geological principals.it main focus is to locate matured and quantifiable accumulation.
Engineering geology focuses on constructions. It is employed in road, dam and building constructions. Various tests are carried out on stones to be used in construction to reduce failure.
Economic geology studies the cost of exploration and exploitation and compares it with the possible cost or value of the reserve (minerals,oil and gas) if the reserve is worth it or not. The sole aim is to make profit.
Marine geology studies the various under sea structures (canyon, sea mount, abyssal plain etc.) and the various plate boundaries in the seas and ocean for their mineralization potentials. Marine geology also studies and proffers solution for water bodies’ pollution and shoreline erosion and land encroachment.
Micropaleontology studies the various ancient micro-plant and animals and uses them to reconstruct and identify ages of rocks and past climates.
Structural geology studies the various structures (fold and fault) produced by the movement of the earth (plate movement) and their implication to engineering construction e.g dam as well as site for mineral accumulation.
I wish this could illuminate the basic aim of each of the described discipline i will welcome contribution/questions from experienced geologist and beginners alike                                                                                     
                                                   SIGNS AND SYMBOLS IN GEOLOGY