A spellheart is kinda like a magic ring with a spell. Kinda. They mostly suck for spells other than cantrips though.
Crafting Rules, which are used for basically all items: magical, mundane, alchemical, or otherwise. It is an alternative way of getting the items rather than just simply buying them. It doesn't really save you any money.
Magical Crafting feat which as mentioned above is needed for crafting magical items such as rings, scrolls, and wands.
Tattoo Artist feat also mentioned above, which will let you create tattoos.
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Rings are a type of standard magical items. They have effects, and sometimes an activated effect of an item will create a spell effect. But that isn't required. There are also rings that don't have activated effects (just permanent effects when worn), or have activated effects that aren't spells. You don't have the option of creating a ring with any arbitrary spell effect on it.
Scrolls and wands are the items that you can pick a spell and put into the item.
It might be helpful of we know more about what you want. Are you playing a spellcaster who wants a re-usable reserve of a spell? A non-spellcaster who wants to have their own pool of spells to cast on themselves? A GM who has players asking for somwthing?
To reiterate points made by others.
There is no guidance for "custom" magic items. By default, you can only make the items published in rules books.
Crafting doesn't nominally save you any money (compared to someone who can Earn an Income at their level). What it does do is guarantee you have an "on level activity" you can do and guarantee you access to (common) items you're interested in acquiring that a GM might restrict due to a variety of reasons (you're traveling through the wilderness for a long time as an example).