True by definition, literally "saying the same". Pointlessly obvious. Additional words that add no meaning.
"Either we'll get in trouble, or we won't" is a logical tautology. By including all possibilities the statement must inherently be true.
In "PIN number
" the word "number" is a tautology because a PIN is always a number. (At least that's what the N originally stood for — if the term PIN evolved to include letters someday then PIN number would no longer be a tautology.)
In "morning sunrise" the tautology is "morning" because sunrises are a subset of mornings; removing the first word removes no meaning. (The addition of "morning" may be aesthetically more pleasing, in a poem for example, but it remains a logical tautology.)