By explaining it

I wasn't raised in religion so I explain that and compare it to I don't believe in the Christian god like a Christian wouldn't believe in Allah. I also like "atheism is a religion like off is a TV channel"

I just tell them if they a xtain that I believe in one less god then they do.

I don't get asked.

I've explained that it isn't hatred of religion or religious beliefs - many religious people who I've talked to believe atheists are evil and mean - it is simply that it is people who find there isn't proof of God's existence therefore they don't believe in Him.

Gnosticism provides three stances:

Gnostic Affirmative ( I know a God exists )
Gnostic Negative ( I know that no God exists )
Agnostic (I do not know any God to exist)
Literally everyone is one of those 3 as this is regarding a claim of knowledge.

Theism provides two stances based on belief:

Theist (I'm convinced, based on x evidence that a God exists)
Atheist (I do not see sufficient evidence that a God exists, and so I am not convinced)

Atheist is regarding a claim of belief which is why you can have Agnostic theists. They don't Know God exists, but they believe it.

Simply ask them if they believe in say: Oden, Zeus, Posiden, Osiris, Mithras or any one of 900 other gods or savior deities. When they say no, they're not real! You say, now you know how I feel about your god and that is ATHEISM... It is nothing more than a lack of belief in a god or gods as there is no credible proof of them.

If they don't understand the simple statement of 'I don't believe in God', then ask then if they believe in Odin, or Thor, or Zeus, or any number or other gods.
Presumably they'll say 'No'. (hopefully they'll also say, 'that's ridiculous'
Then you tell them, 'Ya, that how I feel about (your) god'.

I told my new friend I don't believe in god. That there is no proof there is one. She understood what atheism really is.