Objects are instances of classes.
graph {
node [shape=record]
Class [label=<{<b>User</b> <br align="left"/>| + ID: int<br align="left"/>+ name: String<br align="left"/>+ address: String<br align="left"/>}>]
Object [label=<{<b>deez:User</b> <br align="left"/>| ID = 0044<br align="left"/>name = "deez"<br align="left"/>address = "123 Fake Street"<br align="left"/>}>]
}Attribute (UML Class)
Attributes define the structural characteristics of a class, each instance / object has a different value.
Link to original
Operation (UML Class)
An operation is the behaviour of a class, it is identical for all objects of a class, they are not depicted in the object diagram.
Link to original