What it consists of
A description of something people do now, compiled from published accounts rather than from practice.
Tea served with finger sandwiches, scones with cream and jam, and small cakes, conventionally in that order and conventionally in the mid-afternoon. It is now overwhelmingly encountered as a booked hotel or tearoom occasion rather than as something done at home, and the elaborate tiered-stand presentation belongs to that commercial form.
The origin story, and its status
Repeated very widely and not evidenced. Recorded because the story is itself part of the culture, not because it happened.
The practice is very widely attributed to Anna, Duchess of Bedford, in the 1840s, said to have called for tea and a light meal to bridge a long gap before dinner. The attribution is repeated in almost every account and rests on thin and largely retrospective evidence. TeaHQ records it as a widely repeated origin narrative rather than as documented history.
Afternoon tea is not high tea
TeaHQ's own reading of well-attested general knowledge, with no single source behind it.
High tea was a substantial early-evening meal eaten at a dining table, associated with working households, and it was food-led rather than tea-led. The two are constantly conflated, and 'high tea' is now used by hotels and by overseas venues to mean the elaborate afternoon form — which is close to the opposite of what it meant. The confusion is thorough enough that TeaHQ records the modern usage as a fact about language rather than an error to be corrected.
The cream-first question
A description of something people do now, compiled from published accounts rather than from practice.
Whether cream or jam goes first on a scone is a regional distinction — Devon and Cornwall are conventionally opposed — and it is discussed with a seriousness that is partly genuine and largely enjoyed. There is no correct answer and TeaHQ is not going to supply one.