Polarizers do a number of things.
1) Reduce glare. The effect is most dramatic on highly reflective surfaces, such as metal. See the image below for how big the difference can be.
2) Related to the above, the glare can bolden some colors, but only if the surface is reflective. It will have no effect on cotton or skin, but it does have a noticeable effect on plants, where it enriches the green color.
3) Eliminate reflections on glass or water. You can use it to see into the bottom of shallow streams or eliminate background reflection on windows.
4) Reduce atmospheric haze. The benefit is small here but often helpful. If you're shooting a citiscape or panoramic landscape, you can reduce, but hardly eliminate, some of the poor contrast dust and pollution in the air cause.
---------- Post added 08-16-15 at 01:34 PM ----------
Originally posted by condor27596 When I screw the filter onto lens how do I know what position is best ?
---------- Post added 08-16-15 at 03:21 PM ----------
What is size filter for the 77 ?
Rotate it until you like the effect. You must do this for each shot. If you rotate it fully when shooting something involving sky, you'll find a position where the sky will be almost black. That's usually too much. Dial it back a bit from there. There are positions where everything comes out with a redish tint or cold blue tint. Usually those aren't good either.
The FA77 is 49mm.