All you need to know (and type in) is the parent of each member of the family. The layout will then be completely automatic.
You can enter persons in any order, and add new as you get to know them. Until you get the parents in place, persons will appear on the diagram as unlinked individuals, but as soon as you have the parental information in place, they will be linked into the tree at the proper place.
The basic information is the identification of the individual persons. We use a system inspired by the Danish CPR (Central Person Registration) system. Each person is identified by his/her birth date, together with a sequence number that must be odd for a male person, and even for a female.
You don't have to use actual birth dates, but you should be aware of how this is used. The odd/even data controls the shape of the marker: round for even/female, square for odd/male, and the date values control the ordering of sibs, so that the lowest value goes first from the left.
PediPlot is simplistic in the way that it only keeps track of one parent, but with that limitation in mind it can draw any diagram you might need.
To distinguish genotypes, it gives you access to 12 different markers, that may be round or square depending on the sex of the person. In addition you can use a small and a large rhombus, and a small dot that are independent of sex.
Together with the persons you may store an abstract (free form text) that may be printed with some of the printouts.