Hi!

When i use command
ldapsearch -h ldap.exemple.com -p 389 -x -b dc=exemple,dc=com -L

I get all information about my instance without any authentication
How i can set authentication to this action ?

The term for this is "anonymous binds". How to disable them is mentioned in the relevant guides; for instance if you are running FreeIPA from RHEL/CentOS 8, the RHEL docs refer to:

https://access.redhat.com/documentation/en-us/red_hat_directory_server/11/html/administration_guide/configuring-special-binds#disabling-anonymous-binds

When i  change port
ldapsearch -h ldap.exemple.com -p 636 -x -b dc=exemple,dc=com -L
I didnt get any response
why is that so ?

389 is the default, non-encrypted port; while 636 is the encrypted one. If you want to use encryption, I suggest you use:

$ ldapsearch -H ldaps://ldap.example.com -x ....

Cheers,

Álex