A few designers tend to use the same few references, so keep that in mind.
To find a single point, you enter the coordinates. The coordinates are based on a unit square. i.e. the length of the square is taken to be 1. Halfway would be 0.5, one-third would be 0.333333... etc.
To translate something printed into this scale, divide the distance from the edge (left-to-right or bottom-to-top) by the length of the square.
e.g. if your point is 252.25mm in and 147.75mm up on a 400mm square, your coordinates would be
x = 252.25/400 = 0.630625
y = 147.75/400 = 0.369375
For a line, you put in the start and end coordinates.
After that, you choose "Get references" from the menu.
According to Lang's site;
ReferenceFinder immediately returns the 5 "best" short folding sequences that approximates that point or line. The approximations are very good, often better than 1 part in 1000, which, in my experience, is about the limit of human folding precision.
For each solution, ReferenceFinder reports the absolute error in distance, the rank (the number of folds needed), and the sequence of actions needed to construct the desired reference mark. For more details, read the README.txt file that accompanies each of the download packages.
Generally, crease patterns will have an established sequence for the reference, so there should be one option that has zero error.
Also, if you are measuring, keep in mind that your measurements might be slightly off.
ReferenceFinder can also parse simple algebraic expressions. It helps to know that: √x = x^0.5