Making solutions is an essential skill in chemistry. When accuracy is required (eg, for analytical work), a volumetric flask is used.
You can find more information on using volumetric flasks here.
Stock solutions for qualitative work do not have to be made up in a volumetric flask. A measuring cylinder or a graduated jug will do.
If, however, you are making up a solution accurately, a standard solution, for instance, you will need to make the final sulution up in a volumetric flask. Volumetric flasks are usually pear-shaped, with a flat bottom and can be made of glass or plastic. They have a narrow neck with a ring marked on which accurately marks a specific volume.
The narrow neck allows for greater accuracy when measuring volume. They are filled so that the bottom of the meniscus just touches the line.