1. Get the all the facts about ice-cream

You can first list out everything you can think of about ice-cream

• scoop
• flavour
• color
• cone
• ice cream comes on a cone
• there are different kinds
• multiple scoops can be stacked up.
• etc.

2. Decide on your concept/viewpoint

• there is only one scoop on a cone (there might be one multiple scoops are placed on the cone side-by-side, but my view point is only one)
• there are different kind (flavour)
• scoops can be stacked.

3. Model

The above is the result of modelling.  You then need to start adding various pieces of information like data type, accessibility to this diagram so that everything (almost everything) you would need to write code should be there.