To access the WordPress backend login URL for your website it depends on if you are using the self hosted version, or the hosted WordPress.com.
To access the Admin Dashboard of your WordPress installation, you would use:
Prior to the more recent version of WordPress, you used to access the dashboard VIA <yourdomain>/wp-admin.php. Now, this simply redirects to /wp-login.php.
If you don’t self-host your website and either use their free or paid plan you can visit this link to login.
If you have a self hosted WordPress website, it is a good idea to add an extra layer of security to your WordPress backend login. One of the easiest ways is to add a CAPTCHA to the login form to prevent bot attacks, etc. There are numerous plugins out there that incorporate Google’s reCAPTCHA API and are very easy to set up.
Of course, using a strong password goes without saying as that is your best line of defense to protect your website.