What if someone does not know how to say the prayers? How can he fulfill his obligation? This is a particular problem in situations where the prayers are ones that are said infrequently – like Hallel – so people may not have learned them by heart.
The Mishna on our daf suggests that even an eved (a non-Jewish slave), a woman or a child who has not reached Bar Mitzva, people who are not obligated in Hallel, can lead the prayer, so long as the adult repeats Hallel word-for-word.
Nevertheless, the Mishna rebukes a person who is illiterate and needs to rely on someone who is not obligated to lead him in prayer. If there is an adult leading the prayer, then the person can respond with the word Halleluya and fulfill his obligation in that way.
The Gemara teaches that the tradition was for the congregation to respond to the prayers of the hazzan with a refrain of Halleluya during those paragraphs of Hallel where that was the key word (Tehillim 113-117). In the portion of Hallel where the refrain was different, the congregational response matched that refrain (e.g. Hodu laShem in Tehillim 118). Already during Rava’s time the vast majority of people were literate and were able to recite Hallel without assistance, nevertheless the tradition continued, remnants of which are retained in the recitation of Hallel to this day in many synagogues.
What if someone just listens to the hazzan without responding?
Here the Gemara applies the rule shome’ah ke-oneh – that listening with proper intent is the equivalent of responding.
Tosafot point out that it is certainly better to respond with the appropriate refrain than to merely listen intently, nevertheless there are times when a person cannot say the response aloud and at that time listening may be the preferred option. For example, if a person is in the middle of saying the silent amida prayer and the congregation reaches a place where a community response is called for, the person should remain silent and listen. The rishonim compare this to the case where servants of the king are occupied with their royal service and they cannot take a break from it, even to turn their attention to another important assignment for the king.