How to use JSON-RPC POST request?

I never used JSON-RPC before and a client of mine gave me some API credentials to fetch the info to post on the website. So, I never heard about JSON_RPC before and the only thing I have is this:

curl -s -u MyID:MyPassword -X POST -k --header "Content-type: 
application/json" --data-binary '{"jsonrpc": "2.0","method": "ListOfContent","params": 
{},"id":7123}'

So, given that, how to use it, with what to use it, how to retrieve the data?

An example from here

async function getBalanceUsingJSONRPC(address: string): Promise<number> {
    const url = clusterApiUrl('devnet')
    console.log(url);
    return fetch(url, {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({
            "jsonrpc": "2.0",
            "id": 1,
            "method": "getBalance",
            "params": [
                address
            ]
        })
    }).then(response => response.json())
    .then(json => {
        if (json.error) {
            throw json.error
        }

        return json['result']['value'] as number;
    })
    .catch(error => {
        throw error
    })
}

you can read more about JSON RPC specifications