Question

what is a transformer and how it can help us

Answer 1

Transformer is an electronic device which is used to low voltage into high voltage
There are two types of transformer
1.step up transformer
2.Step down transformer
Step up transformer;-it  used to convert low voltage ac into high voltage ac
Step down transformer;-It is used to convert  high ac voltage into low voltage ac
Note-TRANSFORMER can only work in ac ,fails in dc

Answer 2

It is just a simple apparatus used for reducing or increasing the current... for example you can take voltmeter in your ac!