If the Samba share you're trying to access doesn't allow guest users, you must have an Samba account. This article will show how to create a new Samba user account using the command line.
Create Samba User
Open a terminal window and run the command bellow. Replace
USER with a name for your new Samba user. You'll be prompted for the password to get root privileges, then you'll be asked for a password for your new Samba user.
sudo smbpasswd -a USER