how we distinguish CH3CH2OH and CH3OCH3?

The quickest way is to smell them. Each has a distinctive odor.

A chemical test to distinguish CH₃CH₂OH and CH₃COCH₃ and to heat each of the two liquids separately with potassium dichromate solution acidified with dilute sulfuric acid.

CH₃CH₂OH :
The reaction mixture would turn green.
This is because the acidified potassium dichromate solution oxidizes the CH₃CH₂OH to CH₃CHO, and the acidified potassium solution is reduced to green chromium(III) ions.

CH₃COCH₃ :
There is no observable change as there is no reaction.

Dimethyl ether boils at -24C while ethanol remains liquid up to 78C. There are plenty of other differences, but I don't know the meaning of your question.

By the functional groups.
CH3CH2OH ; the functional group is R- CH2OH making it a primary alcohol.
CH3 - CH2-O-H (Ethanol (Archaically ; Ethyl Alcohol)

CH3OCH3 ; the functional group is R-O-R' marking it an ether.
CH3 - O - CH3 (Methyl methyl ether).

The primary alcohol (ethanol) is oxidised by - and will decolourise (change from purple to colourless) - potassium permanganate solution.
The ether (methoxymethane) won't.