Probably you have to check with your DBA to unlock the account, you need special privilege to unlock the account.
I got an error that my account is locked, i try my best but do not understand what to do to upon my account to connect database I mean to Oracle SQL Developer.
Sql Developer doesn't 'lock' accounts, the database does.
Connect as a user with DBA privileges and issue an ALTER statement to unlock the account. For example for HR use:
alter user hr account unlock;