How can I find the grain of the fabric to sew? Why do I need to know?

I'm an amateur sewer, and I often find sewing projects asks me to know the grain of the fabric. I have no idea how to do this, and have not been able to find any publication that provides easy to understand the answer. Mentioned selvage and parallel to, but what does that mean??! Can anyone explain this to myself, very simple. Also would be useful to know why this stuff when sewing something. Thanks for your help!

Here is a direct quote from my book of padding. "When the fabric is produces yarns are woven in two directions, creating a length and width. This line is called grain. If AC is cut diagonally across the grain (in the triangle pieces) is working on polarization. Blas edges should be sewn and pressed with care, as they stretch easily. The long edges of fabric finishes are called selvages. Always trim off the selvage edges as they can cause distortion of the block and are difficult to hand through the blanket. "Depending on what you sew the block comment probably not apply. However, the selvages are simple white or color the same color as the base material, and generally have the impression on them. If you are sewing garments would not be attractive in use. The length of the grain goes along the shore, while the grain of the Cross goes from bank to bank. The bias of the grains would go to front corners (top left ie the bottom right) of the fabric. Why that matters is the strength of the grain. The grain length is going to be stronger and extend to less than their cross grain. The bias is the weakest point, since it permeates the two grains. Good luck and I hope you enjoy your machine sewing!

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