Wall Socket USB Charger using LM2596S Buck Converter.

Hi,
Sorry n00b here, I was making a wall socket USB charger (5V,3 Amps),I purchased lm2596S Buck converter (Please see the photo attached) The datasheet of LM2596S shows to input "Unregulated DC input" Can you please explain me what I've to attach at that point.? I really don't want to use Big Bulky Transformers before that input.
P.S I want to make it small which fits in that 222 Inches box.
Thanks

Playing with mains is not a job for a noob,
If you have to ask such a question you do not know enough.
Basically you need to convert mains to DC within the range that module requires first. That will take more space than you have.

Thanks for the reply.
I've seen the circuits for mobile phone chargers which is very small and can fit in that space,They also provide 5V and 2-3A.how do they work.?
I want to make something similar with this buck converter,

I want to make something similar with this buck converter,

You can't.
You will need something to turn the mains into DC. This then might as well be something that turns mains into 5V in the first place so your buck converter has no job to do.

I've seen the circuits for mobile phone chargers which is very small and can fit in that space,They also provide 5V and 2-3A.how do they work.?

They work by what is known as a switch mode circuit which is similar to your buck converter.

Design and building of such a unit is way beyond your skill set. Power supply design is a specialist branch of electronic engineering. I have been doing electronics for about 50 years and I would not attempt such a thing.

Buy one like everyone else.