To be means to exist, to live. Being there is to live with one's full presence in the present.
To be with someone is to be silent inside and to be in rapport.
If you should find yourself day-dreaming, gently draw your attention back into the present.
When you sit in full presence with another there will be no expectations from you about what "they" should be doing. There is no requirement for anything in particular to happen or not happen. Just "being" with another allows you the gift of their presence in that timeless moment.
Give yourself the gift of complete attention to someone without the need to do or say anything in particular.
If you have pressing physical needs such as hunger or need to use the bathroom either wave these concerns aside or handle them and return. It is better to take a few minutes break to handle a distraction then to spend hours distracted.