I'm trying to get the hang of this and try to understand the transaction process, how it works, how to verify it is it safe, etc I've been reading about it and can't understand fully.

My BitCoin Address:

1NmJWy38tVHk1pTZAr67CTVyPzPAkzMKn7

Can anyone send me any amount, smallest amount even, I will send it back. Does it just go through to my address? Do I have to sign something, how do you make a trade where if you send money to someone, and he wants to send you something, how do you make the trade safe? Rather than one goes first.. Or is that how it works?

Thanks !