Mouldings are not only decorative but improve the features of the room. Walls can be sectioned by them, thus we feel the low ceiling higher, but they also help section the too high ceiling, making it more acceptable for the eyes. Frequently the spaces between mouldings are painted in different colors or they get different coverage.
In old times, mouldings were made of hardwood or gypsum. Most of them was richly carved which complemented the architectural elements. Nowadays they are mass produced, made of paintable polystyrol. This can be placed very easily and can be bought in several sizes and patterns.
Baseboard is placed downmost, at the junction of the floor and the wall. Its back side is straight, this slicks to the wall. It is made of wood or fiberboard, which can be painted easily also, but for wet rooms there are many pieces in tile-collections. The dimensions of the baseboard are specified by the scales of the room, commonly 8-12 cm high (but maximum 20 cm). Its task is hiding the floor’s bumpiness and protecting the wall from e.g. scratches by legs of the chairs.
Dado rail is set up at 85-90 cm. The wall-part below it is frequently paneled, which protects the lower part of the wall from damaging impacts. Its height anno was equal with the height of chair backs (chair rail), so it was suited for protecting the wallpaper or painting when chairs were pushed against the wall. Later it had rather just a decorating role.
Picture rail is a fully functional element:  big, framed paintings are hanged on it with wires and hooks. It holds their weight and this way the plastered or gypsum-decorated walls are not damaged. It is placed between 210 and 270 cm depending on the height of the ceiling.
Crown moulding is placed at the junction of the wall and the ceiling. It gives finiteness and frames the room. Exact mitering in the corners is essential for the esthetic, perfect fitting of the two parts. The cross-section of cornice is a right-angled triangle, they are being pasted up in just right the corner. Because they hide the joint of the vertical and the upper horizontal planes, they raise the feeling of height.
We can use other, similar decorating elements beside the basics. Ask for help of an interior designer for planning.