Brief
Tell us what the container has to do
A good brief answers the same questions the moulding cycle asks: what it holds, how much, in which material, how it closes, in what colour, and how many. Answer what you can; "not sure" is a useful answer too.
Why each answer is asked
Decides the material before anything else. Oils, solvents and acids rule some plastics out; food narrows the grades to ones declared for food contact.
Hot filling, freezing and a microwave each ask something different of the wall. A container that is fine at room temperature can soften or crack at either end.
Points to the family and to whether a shape that already exists could do the job, which is the difference between weeks and months.
A snap lid, a thread and a tamper band are all cut into the mould. Knowing which one is needed early saves redrawing the rim later.
Tells us whether a shared shape is enough or the work justifies its own mould, and how the parts should be packed to travel.
Only to answer you. Nothing you write here is used for anything else; the details are on the data page linked above.