Dynamic page loading in javascript-JS

I am a beginner. What I am doing now is that after a student logs on, he can see the most recent activities (start time, location, and participants) in the school. He can choose to participate, once the participants are full, they will not be able to participate. That's easy. The problem is: I am now using PHP at the backend and js dynamic at the front end. I don't know from the data...

I am a beginner. What I am doing now is that after a student logs on, he can see the most recent activities (start time, location, and participants) in the school. He can choose to participate, once the participants are full, they will not be able to participate. That's easy.
The problem is: I am now using PHP at the backend and js dynamic at the front end. I don't know what data formats should be used for sending back JavaScript data from the database (easy to learn, the pursuit of efficiency does not consider performance), and then what method is used to insert elements into the page (is DOM convenient and easy to typeset )?

Now is the front-end page I just created

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I am a beginner. What I am doing now is that after a student logs on, he can see the most recent activities (start time, location, and participants) in the school. He can choose to participate, once the participants are full, they will not be able to participate. That's easy.
The problem is: I am now using PHP at the backend and js dynamic at the front end. I don't know what data formats should be used for sending back JavaScript data from the database (easy to learn, the pursuit of efficiency does not consider performance), and then what method is used to insert elements into the page (is DOM convenient and easy to typeset )?

Now is the front-end page I just created

Json is the most convenient,