Site preferences

You can refine certain site preferences in the Site settings > Template > Advanced > Site preferences tab.  These preferences are as follows:

E-commerce checkout via
The checkout options are:

PayPal
This is the easiest option to use (recommended) but does not allow adding shipping and tax rules.

Mals-e
This allows setting-up shipping and tax rules, but requires an account at mals-e.com.  Once set-up, you'll need to enter your Mals-e username and server name here as well.

Force https://
This forces your page to always load at https://, which will eliminate the Not secure warning displayed by some browsers.  Your site must have been live at yoursite.com for 48 hours to use this option.