How do you teach your younger siblings? I have a sibling who is dumb.

Calling a relative dumb is not cool. If you judge others, you are not a good person. My brother has Autism and ADHD and I don’t call him dumb. I help him overcome his difficulties, by explaining things step by step. There is no such thing as dumb. It is just a way to make yourself feel and look more inferior.

?

That is rude. Your sibling could literally be a genius but lack social skills (which is common in geniuses) or have a mental disability. Be cautious about how you go about this and talk to your parents about getting him/her checked out.