The inessive is always formed with the suffix ssa or ssä, but the stem often changes, in ways described elsewhere in this book. Moreover, in plural, the inessive suffix is preceded by the plural suffix i. Example: kukka : kuka|ssa : kuk|i|ssa (flower : in flower : in flowers).
The inessive usually refers to being in (inside, within) something, in a concrete or abstract sense. Examples: talossa (in a/the house), tammikuussa (in January), vaikeuksissa (in a trouble; literally: in difficulties). Regarding its use to express time, see Expressions of time.
The inessive thus mostly corresponds to the preposition “in”, but may also correspond to e.g. “at”, e.g. koulussa corresponds to “at school”.
The inessive is also used in contexts where it means being in close contact with or attached to something, as in käsineet kädessä (with gloves on; literally: gloves in hand). Section Locational cases covers such uses of the inessive as well as other idiomatic usage.