There are 2 steps required to make your Wordpress website uses HTTPS (SSL) connections by default:
before continue, be sure that your SSL certificate is already installed, in most cases its already installed automatically, test your website first using https, you may see some errors, but it will be OK for now.
1. Configure Wordpress to use HTTPS urls from your Wordpress admin area > settings > General
and use https URLs as below
Now all your website links generated by Wordpress will use https, but just typing the domain in the browser, the normal non-https website will be loaded by default, lets fix it: