You can drag a selection box to select adjacent particles, or you can Shift-select non-adjacent particles. The particles turn yellow when selected. If the particles don’t become selected, make sure the selection mask is set correctly for particle selection. See Basics for details.
The particles are abbreviated pt, pt, pt, and so on. The number in brackets is not the particleId. It’s an array index used internally by Maya. If you want to be certain you’re setting the value of the correct particle, select only that particle in the workspace. The Component Editor displays only the selected particle.
The value you enter becomes the initial state value—the value of the attribute at the first frame. Unless dynamic effects alter the value of the attribute, this value is used for the entire animation. See for more details.
Many per particle attributes have vector values. A vector is a related group of three components. For example, velocity is made of velocity X, velocity Y, and velocity Z components. As another example, rgbPP has a vector value made of R, G, and B components. These are labeled rgbPP, rgbPP, and rgpPP in the Component Editor.
If you’re unfamiliar with how to use vector components to set position, velocity, or acceleration, experiment with the various component values until you develop an intuitive sense of their effect on motion.