A commit is a recorded point in your project's history: a set of file changes, an author, a message, and a timestamp. It is the atomic unit of version control. Everything you can restore, compare, or audit is anchored to one.
On a text project, a commit stores a diff, because storing the handful of changed lines is far cheaper than storing the file again. On a game project, most commits store complete files, because computing a meaningful diff of a binary asset is not possible and attempting it produces something both large and useless. This is why game source control is more storage-hungry by nature, and why unlimited storage matters more here than in software engineering.
Good commit practice on an art-heavy project differs from code habits in one important way: the message has to carry more weight. Nobody can read the diff of a texture to work out what you meant, so the message is the only record. "Retextured the market stalls, warmer palette per art review" is useful in six months; "updated assets" is not.
Commit frequency matters more too. An uncommitted afternoon of binary work is genuinely unrecoverable if a drive fails, because there is no partial state to salvage. Commit at natural milestones during the day, and always before you stop.
In USourceControl a commit both records the change and pushes it to the server. There is no separate local-commit step, so once it succeeds the work is safe.