It means what it exactly implies as in to start collecting something whatever you would like to add to your collections, during your spare time or vacation such as collecting currencies from the countries all around the world and so on.

When I was 10, I used to collect stamps of around 65 different countries and this collection still takes me to those sweet childhood memories.

It is considered to be one of the people's hobbies at all the time.

Help please

Start a collection

What does this phrase mean?

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There is a second meaning.

In this country it can also mean to collect money - for a charity, or for a worthy cause.

For example:

(at work)

I just heard that Fred is getting married next weekend. We had better start a collection. (in order to give Fred and his bride a wedding gift).

It could even be used sarcastically.

(two friends talking)

A: Did you see the news story about the bird with two broken wings, it was terrible ...

B: Oh, go start a collection .... Me, I'm saving my money for a hotrod/holiday/donation to Greta Thunberg.