It depends on how the yard is set out. The points on the main line would be classed as junctions. Once you are in the yard area proper, it depends on the layout. Often, groups of sidings are given distinct names, Example - "Coal" and "Merchandise", or "Bill" and "Mary" (honestly!) and the points would be numbered / named accordingly. On the main line, as for the actual numbering, there is always a "system", but there is no standard rule. Generally, you can go North South, or vice-versa, or start with the main junction and fan outwards. The main convention is that cross overs have pairs of points, and these are numbered in pairs xxA and xxB. In complex areas, there might even be xxC, xxD etc. With loops, in real life, there is no rationale. However, it makes sense to number the points on a loop in pairs - so xxI for In and xxO for Out. Or xxE (east end) and xxW (west end). The main thing to bear in mind though is to try use a system that is easy for YOU to remember.