There are lots of units in electronic,
Ampere- This use to measure the flow of current.
Voltage- This one is use to measure the potential difference between two terminal.
Each unit is derived with the help of ohms law.
Flux, flux density, charge,ohm, Faraday, Henry etc are very important units in electronic.
Yes you saved money if you directly order from Chinese site, but you should have a lots of things not one goods you and yo get it, there is tax when one country export to another country.