Setup
The Setup process for Cumulus is briefly mentioned in the 'readme.txt' and covered in detail in the help files. Once Cumulus is installed: Click Start, Programs, Cumulus and select the Help. Expand the Introduction section and begin reading at "Getting Started" until you have got everything working.
In addition to the help, there is a handy installation guide here
Configuration: Settings
Configuration settings information for your particular Cumulus version/build is in the Cumulus Help.
The information in cumulus.ini describes all initial configuration settings for the latest Cumulus release (and may mention some additions established in beta builds, other than any experimentations just being trialled in a special or beta build). There are other configuration files for more sophisticated options such as how Cumulus communicates with external reporting systems.
You may find the Cumulus_Screenshots help you, although note the screens were recorded in the past, and therefore the ones shown may relate to a different version to that you are using.
Units of measure
By far the biggest decision you will make, and be held to, is the various units of measure. Select these very carefully when you are setting up.
Remember if you try to change your old data later it probably has already been rounded and applying a single conversion factor would cause inaccuracy. For instance in rainfall you can't get back exactly to millimetres to 1 decimal place from inches to 2 dp. For example, 0.01 inches is 0.254 millimetres, which rounds to 0.3 mm, but 0.02 inches is 0.508 mm, which rounds to 0.5 mm rather than 0.6.
To minimise rounding error, you need to convert the old data first into whatever precision your weather station works in (e.g. Fine Offset rainfall bucket is 0.3mm, its pressure measurement is in dPa (integer decaPascal), wind speed in tenths of metres/second and temperature in tenths of degrees Celsius), this may be different to how you have set its console display, and then convert into whatever future units you select for Cumulus before rounding. So devising suitable conversion tactics and applying to all old data could require hours of work. See this thread and others in support forum.
Dates
Cumulus does require your computer SYSTEM short date to use a format with a separator between day, month and year in whatever format suits your region e.g. dd/MMM/yy, dd-MM-yy, MM/dd/yy and dd-MMM-yy are acceptable, but ddMMMyy is not suitable as a short date format with Cumulus. Any change to your short date format later is likely to give problems.