The idiom 'it does exactly what it says on the tin' is a popular phrase that was made famous by an advertisement campaign in the UK. Its meaning is that the name of something describes a product or the qualities of something accurately. Something that 'does what it says on the tin' doesn't have a hidden agenda and works as per instructions.

1. Tom: What did you think of that paint we got? Kate: I loved it, it did exactly what it said on the tin.
2. I bought a new laptop and the specs are brilliant. It does exactly what it says on the tin.