What is a quote from Shakespeare's The Merchant Of Venice that shows Nerissa helping Portia in something?

Nerissa helps Portia in many ways. She's not the type of servant who brings Portia her food or cleans up after her, necessarily. She's not a cook or a maid. She's more of a lady-in-waiting, which is something like a personal assistant in today's world. For example, Nerissa acts as a mediator between guests who want to see Portia. She tells Portia who is at the door and either admits them to see her or turns them away. Nerissa can also act as a messenger by carrying notes or letters back and forth for Portia's business or social purposes. In fact, Nerissa even goes so far as to disguise herself as a law clerk when Portia pretends to be a doctor of the law in Act Four. It is Nerissa who approaches the Duke in disguise as a law clerk and presents him with a message from Portia that explains why she is there to help with the legal proceedings. The following shows Nerissa helping Portia as her servant by delivering the message to the Duke:

"'Came you from Padua, from Bellario?'

'From both, my lord. Bellario greets your grace'" (IV.i.118-119).

The stage directions that accompany this dialogue is "She gives the letter to the DUKE. SHYLOCK whets his knife on his shoe." Therefore, Nerissa acts like a personal assistant by delivering messages for Portia, and this scene in Act 4 clearly shows her doing that exact thing. Throughout the rest of the scene, Nerissa stands in the background, ready to help Portia with anything she may need.