I don't want to "sign in" with my password..every time I open my computor.

Any chance you have an Apple Watch?

If so, your Apple Watch can serve as authentication. Unlock your Mac with Apple Watch - Apple Support

But otherwise, it's not smart to leave your MacBook Air with no security at all, as Urquhart1244 has mentioned.

You should want this security, especially as a MacBook Air is a mobile computer, easily carried to different places, that could be left unattended for some time in semi-public spaces (e.g. office), and others should be locked out in such situations, even in places where theft isn’t the first concern.

1. Automatic login (after shutdown-startup or restart) is not available in combination with FileVault (disk encryption).
2. Log-in can be optional after Sleep Mode (Set Require password to: never). See System Preferences.