Religions in Civilization 13 are custom-made, and as a founder you can choose its symbol, colors, focus, clergy organization and so on. First, you will need to maximize the philosophy skill. You can do it by either reading books by other people or writing them. Only with 2.5 philosophy will you be able to create a new religion! Then, click on Create Religion under the Faction tab.
The symbol you choose will be the one featured in the holy books, as well as the totems and structures. The color will be the primary color you choose, while the secondary color will be the background one.
Knowledge-focused religions give a 25% modifier when writing/reading books. They give a 15% modifier when researching.
Combat-focused religions give a 10% buff to combat skills.
Production-focused religions give a discount when building things. The discount is of 1 when building anything with a cost between 4 and 9, and 2 for 10 and above.
When choosing the Clergy Organization type, you will be able to choose the way your religious leaders act and what advantages and disadvantages they have.
Requirement to join the Clergy: NONE
Religious power acquisition: Totems
Shamanistic religions have the advantage of anyone being able to become a Shaman. Shamans have a buff on medical skill (they will learn it twice as fast), so they make good healers. Totems built around the map increase the religion’s power.
Requirement to join the Clergy: NONE
Religious power acquisition: Sacrifice of Infidel Iconography
Cult-oriented religions, like Shamanistic religions, have the advantage of not having a minimum philosophy requirement to become a member of the Clergy. Cultists are also hidden from other religions (they don’t get the honorific title attached to their names), and can recognize each other. Destruction of non-cultist iconography (holy books, talismans) at an altar will increase their religious power.
Requirement to join the Clergy: 1.75 Philosophy
Religious power acquisition: Worshiping Sessions
Religions with Priesthood have the advantage of priests being able to recruit without a Holy Book (needing only an altar). Priest-oriented religions can also increase power by holding public worshiping sessions near an altar.
Requirement to join the Clergy: 1.5 Philosophy
Religious power acquisition: Filled Bookcases
Religions with Monks have a big focus on knowledge - Monks will have learning buffs, will be able to produce research books faster, and can copy Holy Books without the need of a printing press.
Requirement to join the Clergy: 2.2 Philosophy
Religious power acquisition: Conversions
Religions with Clerics, despite having very high requirements for Clergy, enable all ordained members to write Holy Books - effectively enabling the religion to spread under persecution where all the original works are destroyed. Contrary to other religions, members cannot leave clerical religions. Conversions will increase religious power greatly.
The religion’s holy book is the main means of converting outsiders. Holy Books can only be written by the founder (except in the case of Clerical religions). These books can be copied using printing presses (or, in the case of Monk religions, by hand), but be aware that if all the books are lost, you might not be able to expand the religion further!
Posters and Altars can be built. Some styles of religion might rely more on these, like the Shamanistic religions with totems and Priesthood religions with altars.
A list of all altars, note that there is no difference in any altar so you can make the one you like the most or fits your temple.
Wood altar. Made from wood.
Stone altar. Made from stone.
Marble altar. Made from stone.
Bamboo altar. Made from bamboo.
Iron altar. Made from iron.
Obsidian altar. Made from obsidian.
Sandstone altar. Made from sandstone.
A list of all statues of both stones, its good to know them if you want to make an animal themed religion.
Amulets and Talismans enable the wearer to get the religion focus advantages.
Converting people is important to expand your religion, and its so simple it seems easy, but have in mind its also so slow people will prefer to keep doing ~nothing~ their work.
Converting people is simple, but as said before its really slow and tedious, more if you have a lot of people.
The slowest way of converting. To convert someone to your religion you have to give them your book, suposing a risk for the religion since they may be cultists looking to burn your ideology. If they are clear and really want to join your religion they will have to read it, for that, they have to stand still for 1 minute and 30 seconds, so first take them to a private place whit no people.
This is the most optimal way and the only reason why most religions are priesthoods. To convert someone you need a priest religion, an altar, made of multiple materials. First, make them stand still on top of the altar, then a priest has to use the altar, while the converted person is on top of it and they will be converted instantly.