The pH of a solution depends on the concentration of hydrogen ions, H+, in it. The more hydrogen ions there are in each dm3, the lower the pH. Acids release hydrogen ions when they dissolve in water, which is why acidic solutions have a pH below 7.
In a neutral solution, such as pure water, the concentration of hydrogen ions is balanced by the concentration of hydroxide ions, OH-, and the pH is 7. In an acidic solution there are more hydrogen ions than hydroxide ions, so the pH is below 7. In an alkaline solution there are fewer hydrogen ions and more hydroxide ions, so the pH is above 7. At GCSE we use whole numbers of pH only.
This explains what happens in neutralisation. If you add an alkali to an acid, hydroxide ions react with hydrogen ions to make water. The hydrogen ion concentration falls, so the pH rises. When the pH reaches 7 the solution is neutral. Adding more alkali then makes the pH go above 7.