old is used to describe something that is not current, to describe something of a certain age, or to describe something that is no longer functioning or useful.
rules and use cases for this part of speech include things like describing age (e.g. an old car), comparison (e.g. an old model), rank (e.g. an old school student).
1. The old church was built in 1746.
2. The old man's face was full of wrinkles.
3. She bought an old laptop for a cheap price.
Tips and common mistakes:
When using old as an adjective, it is important to provide context for what the old thing being referred to is. It is also important to note why it is considered old (not current, old age, no longer useful, etc).