You start by taking a sheet of paper and listing all the different entities
that represent your system: Equipment, Equipment Types, etc. Once you have
that list made, get another sheet of paper and list all the possible
attributes (fields) that relate to each of those entities. Next, you need to
determine how the various entities are related to each other. Once you get
all that done, come back and someone will be able to help you take the next
step.