We recently started with locus in Maths. Analytical Geometry to be precise, and I while I don't find it too hard, I do have a few questions about it.

1. How do you know when exactly the locus is a circle, or a parabola, or a straight line, etc? Can someone give me a few tips on this?

2. Are there any interesting things we can do with a locus? Or are they just used to find a point that is just as far from point A as point B...

3. What is the plural of locus?