An assignment is simply setting the value of a variable.
Assignment statements are always in the form of VariableName = Value:
FirstName = "Joe"
YearsAsProgrammer = 22
BirthDate = BirthDateField
In the first two examples, I used literal values to set the variables. In the last example, I used another variable to set the variable.
Assignment statements can get a lot more complex, because you can use more complex expressions on the right side of the assignment.