What you should be able to do.
WHAT TO LEARN
Update text on a page Add a page or a product Upload and resize images Check enquiries or orders Update plugins, or know who does
WHAT TO ASK FOR
Training at handover, and written instructions.
WHY IT MATTERS
Depending on a developer for a text change is slow and expensive.
And if they become unavailable, you cannot maintain your own site.
WHAT NOT TO TOUCH
Theme files Configuration files Anything you do not understand
WHAT TO ALWAYS DO
Back up before any significant change.
WHAT TO ASK ABOUT
Whether updates are your responsibility or theirs.
That must be explicit.
IF IT IS YOURS
You need to know how, and to actually do it.
An unmaintained site is a compromised site eventually.
WHAT TO PRACTISE
Making a small change while the developer is still available to help.