The following example defines a new Field object and appends it to the Fields collection of a TableDef object:
Sub NewField()
Dim dbs As Database, tdf As TableDef, fld As Field
' Return reference to current database.
Set dbs = CurrentDb
Set tdf = dbs.TableDefs!Employees
' Create new field in Employees table.
Set fld = tdf.CreateField("SocialSecurity#", dbText, 11)
' Append field and refresh collection.
tdf.Fields.Append fld
tdf.Fields.Refresh
Set dbs = Nothing
End Sub