A religion normally has some stories, beliefs, practices and symbols that help make sense of things. The kinds of questions religions typically answer include:
How did we come to be?
Why are we here?
Why do we suffer?
How should we act?
What happens when we die?
The stories may be seen literally or figuratively but they'll generally try and address these questions and tie them to beliefs. The stories might be about times past, or they might present a perception of present times, or predict times in the future.
The practices will normally claim to elevate people -- make them happier, better off. The symbols are reminders of the stories, beliefs and practices. They could be physical (people, places, objects) or conceptual (dates, words, ideas).
A very important element of religions is taboo. Taboo lists things we must or must not do or say or think in certain circumstances. It surrounds rituals, symbols and beliefs and makes them sacred. Breaking taboos normally incurs fear, anger, displeasure among the faithful and often requires punishment or atonement.
Taboos often lie around food, reproduction, birth, particular ages, genders, death, places, tools, words, elements and nature.
Religions often include gods or spirits or other metaphysical characters from religious narrative that are imbued with sacredness (and hence, surrounded by taboo).
Religions are often deeply embedded in culture and politics. They're typically tied to economies (influencing how people make a living or how they do their work, and often benefiting from the work done), politics (influencing who gains power and how, or ratifying the power they gain, and themselves suffering schisms), the stages of life, societal conflicts (wars, rivalries, espionage) and a society's history.
Here's a quick, synthetic religion-sketch as an example. This faith I call
Moribo -- the religion of Design.
How did we come to be? We are rejects from a cosmic experiment
Why are we here? This is the place where imperfect things are discarded
Why do we suffer? Because our imperfection creates inefficiency
How should we act? Toward greater efficiency
What happens when we die? Our Assembly is dismantled but our Design remains. Our Design may be Reinstantiated into another Assembly and Retested until we achieve Optimality and depart the world of Refuse.
Holy symbol: The Design, a kaliedoscope of interlocking coloured pieces
Holy practices: Creation of representations of the Pattern; analysis of the human Design, eugenics; Diagnosis: an acknowledgement of our Inefficiencies; Recalibration: repetitive, menial tasks that redress our Inefficiencies
Taboos: Don't suffer deformities to live, for their Inefficiency is a pollutant; Waste nothing -- not words, nor food, nor materials; Never repeat the same task unless Calibrating; never flee Adversity, but master it.
Political Influence: Moribo tends to favour meritocracies and oligarchies, where candidates are tested for their physical, mental and genetic superiority.
Economic Influence: Moriban societies tend to love automation, education, training and frequent testing.
Military Influence: Moriban societies tend to be aggressive, warlike and weak in diplomacy. However, they treat their conquered people well --
if they meet the Moriban standards of health, fitness and intellect. Moriban societies practice eugenics on themselves and are not squeamish about inflicting it on the societies they conquer.
Ceremonies: Moriban ceremonies revolve around Testing and Acceptance. Key passages of life: birth, puberty, adulthood, marriage undergo extensive testing and celebration of acceptance. Death however is treated perfunctorily; bodies are recycled and the deceased's possessions are Reviewed for reuse.
Schisms: Moribo is divided into three major sects: The Prospectives are concerned about planning for the future; they are tolerant of Inefficiency today. The Conservatives are concerned about minimising existing waste. The Determinists are concerned with removing choice as much as possible.
Hope that helps.