The Setup process for Cumulus is 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"
In addition to the help, there is a handy installation guide here
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 as changing them later is not advisable and could require hours of work to change your old data.