Is there someone who wants to help me?
I cannot find any differences but structures in them.
Can I use any sentences with " although" instead of " whereas/ while" ?
For examples; Although it was rainy, he didn't take an umbrella. Is it possible to say: He didn't take an umbrella whereas it was rainy.
'whereas' means 'in contrast to, or in comparison with something else'.
"I found the people in France to be very rude to foreigners, whereas people in the other European countries I visited were all exceedingly friendly."
There is no comparison being made between two things in the sentence you suggest:
He didn't take an umbrella whereas it was rainy.
"This umbrella is suitable for use(noun) / to use(verb) when it's raining whereas this one (umbrella) is not waterproof and meant to be used to keep the sun off one's face."