What it means
合う is an intransitive verb meaning that two things fit, match, suit each other, or go well together. The thing that fits or matches is commonly marked by が, while に or と can identify the person, object, or counterpart involved. Attached to a verb masu-stem, 合う forms a compound meaning that people do something mutually or together, such as discussing something with each other.
Usage note
合う is intransitive, so the thing that fits or matches is not marked by を. Do not confuse the compound ending 合う with the independent verb 合う: the compound expresses mutual action, while the independent verb describes compatibility or a good fit.
How to use it
この料理が白ワインと合います。
This dish goes well with white wine.
この色が部屋の雰囲気に合います。
This color suits the atmosphere of the room.
その靴のサイズが私の足に合います。
The size of those shoes fits my feet.
参加者は意見を出し合います。
The participants exchange opinions.
この料理が白ワインと合う。
This dish goes well with white wine.
この色が部屋の雰囲気に合う。
This color suits the atmosphere of the room.
その靴のサイズが私の足に合う。
The size of those shoes fits my feet.
参加者は意見を出し合う。
The participants exchange opinions.