introducir vs presentar
'Introduce' someone is presentar. Introducir is to insert or bring in something new.
presentar
To introduce people, present an item, or submit something formally.
Te presento a mi hermana.
Let me introduce my sister.
The standard introduction. Presentar a + person.
Se presentó como ingeniero.
He introduced himself as an engineer.
Presentarse = to introduce yourself or to turn up.
Presentó la denuncia ayer.
She filed the complaint yesterday.
Presentar = to submit or file a document.
introducir
To insert, enter data, or bring a new thing into use.
Introduzca la tarjeta en la ranura.
Insert the card into the slot.
Instructions language. Formal imperative.
Introduce tu contraseña.
Enter your password.
Entering data into a system.
Introdujeron cambios en el reglamento.
They introduced changes to the rules.
Bringing in something new, not a person.
Tricky bit
'Te introduzco a mi madre' is a common slip and sounds odd or even comic. For people, always 'presentar'.