A laser level is used to project a constant and common level line of light onto a surface on a horizontal or vertical plane. This is most useful in transferring a level from one place to another as is required, for example, when fitting picture rails or dado rails to the wall of a room.
There are many different types of leveling devices but a laser level will consist of a device which incorporates mainly a spirit level or pendulum level with the use of a laser to find a constant level line over distance.
This type of laser level is a fixed laser level that is fixed in a set position to project a level line of light. It is just for projecting a straight line of light on a single plain from which markings can be made for positioning or using for calculations.
This type of laser level simply points a laser spot at the wall which you transfer by moving the head of the laser. They are very simple to set up and use (Have a look at the video below).
As they are less sophisticated than other types of laser level, they tend to be cheaper and simpler to use. They are less versatile and are ideal for periodic use at home rather than continuous use on site where a more fully featured device might be preferred and warrant the extra cost.
Spot levels are used to transfer a level round the room for 1 item, perhaps getting a new socket to line up with the existing sockets. Spot levels are ideal in the garden; laying a patio to the correct fall for example.
This is a slightly more advanced levels than the spot or line level as it will project a cross on to the wall. This is very useful of you need to make sure that you have a vertical line as well as a horizontal level line.
It is a static laser which you move by hand to transfer a point or continuous line from one side/end of a room to another while another line at 90° to the horizontal line is shown on wall. This is slightly more complex than a simple spot or point laser level, so it does take marginally more setting up, but most models are very simple to use these days. They do tend to be a little more expensive but they allow you to get the job done a little more easily and quickly.
Like the fix or spot laser level the cross line level is ideal for putting up shelves, pictures and hook; anything that you need to attach to the wall and that must be level. A line level is good for seeing at a glance how level the wall you are building is and how it corresponds to the wall you need to build on the other side of the garden or the top of the fence.