It is prescribed in Islam to offer condolences to the family of the deceased. This should take the form of whatever is thought will bring them consolation, stem their grief and help them to be patient.
Condolences should be offered in the manner reported from the Prophet (peace and blessings of Allaah be upon him) if one can remember that, otherwise in whatever good words come easily to one which will achieve the same purpose and which do not go against Islam.
It was narrated that the Prophet (peace and blessings of Allaah be upon him) said: Lillahi Maa Akhadha Wa lillahi Maa a3taa Wa Kullun 3indahu ilaa Ajalin Musamma Fasbir Wahtasib “To Allaah belongs that which He has taken and that which He gives, and with Him everything has an appointed end, so be patient and seek reward.” Al-Bukhaari

Two things must be avoided:

Gathering to offer condolences, even though the people do that.

The family of the deceased preparing food to offer to those who come to offer condolences.

The Sunnah is for the relatives and neighbours of the deceased to make food enough for the bereaved family. Wallahu A'lam

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