1. See response to question 2.
2. https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/s3-example-creating-buckets.html - the documentation is perhaps more beginner friendly
3. Depends on your use case. GetObjectCommand is the straightforward method, but you'll run into premission issues most likely. A presigned URL is a URL that you can provide to your users to grant temporary access to a specific S3 object.

Here's code for GetObjectCommand using getSignedUrl (I've also updated the doc.)

const {
    S3,
    CreateBucketCommand,
    PutObjectCommand,
    GetObjectCommand,
    DeleteObjectCommand,
    DeleteBucketCommand,
} = require("@aws-sdk/client-s3");
const { getSignedUrl  } = require("@aws-sdk/s3-request-presigner");
const fetch = require("node-fetch");

// Set parameters
// Create random names for the Amazon Simple Storage Service (Amazon S3) bucket and key.
const params = {
    Bucket: `test-bucket-${Math.ceil(Math.random() * 10 ** 10)}`,
    Key: `test-object-${Math.ceil(Math.random() * 10 ** 10)}`,
    Body: "BODY",
    Region: "REGION"
};

// Create an Amazon S3 client object.
const s3Client = new S3({ region: params.Region });

const run = async () => {
    // Create an Amazon S3 bucket.
    try {
        console.log(`Creating bucket ${params.Bucket}`);
        const data = await s3Client.send(
            new CreateBucketCommand({ Bucket: params.Bucket })
        );
        console.log(`Waiting for "${params.Bucket}" bucket creation...\n`);
    } catch (err) {
        console.log("Error creating bucket", err);
    }
    // Put the object in the Amazon S3 bucket.
    try {
        console.log(`Putting object "${params.Key}" in bucket`);
        const data = await s3Client.send(
            new PutObjectCommand({
                Bucket: params.Bucket,
                Key: params.Key,
                Body: params.Body,
            })
        );
    } catch (err) {
        console.log("Error putting object", err);
    }
    // Create a presigned URL.
    try {
        // Create the command.
        const command = new GetObjectCommand(params);

        // Create the presigned URL.
        const signedUrl = await getSignedUrl(s3Client, command, {
            expiresIn: 3600,
        });
        console.log(
            `\nGetting "${params.Key}" using signedUrl with body "${params.Body}" in v3`
        );
        console.log(signedUrl);
        const response = await fetch(signedUrl);
        console.log(
            `\nResponse returned by signed URL: ${await response.text()}\n`
        );
    }
    catch (err) {
        console.log("Error creating presigned URL", err);
    }
 
};
run();