How could someone create a Facebook account with my email address without stealing it?

Besides the fact the facebook account could have been created there is also the posibility that the emails are phising attempts that only look like they are coming from facebook.

So do not follow links in the emails, it may not be facebook they go to.

The idea in another answer to reset the password to prevent the account from being accessible by those who created it is good, but go to facebook directly to do it. You may find out that facebook have no knowledge of the email address (a recover password mail may never appear).

If you follow a link in the mail and alter the password to your usual password, you may very well just have given phishers access to all your online logins.

In Facebook its possible to create account with another person email, but your account still unverified until you use one of the verification methods (phone, another email).

The account can even be activated/verified if the real owner of the email address accidentally confirms by clicking on the link.

Just go to the login page, and use the password recovery facility to change the password, then log in and disable the account. Then no one can create another account with this email address.