How to draw and give functions to multiple things at once?

This is a very hard question to answer since there are many things which come into account when you have to deal with these things.

What I usually do, is that I set up an array for all my enemies. Each enemy is basically an object with values such as their coordinates, direction, sprites etc., and what's most important, a draw() and an update() function.

In my main game loop, I usually have two cycles. One for updating the behavior of the enemies based on the player's location for example, and the other to actually draw them onto the canvas.

//A simple enemy object
function simpleEnemy(){
    this.x;
    this.y;
    this.sprite;
    this.update=function(){
        //Any logic which decides where the enemy will be in the next frame
        //This, in the end, just updates the X and Y coordinates of this entity
    }
    this.draw=function(){
        ctx=gameArea.context;
        ctx.drawImage(this.sprite,this.x,this.y);
    }
}

//The main game loop
function updateArea(){
    gameArea.clear();
    //Any update and drawing function you have also comes here
    for(i=0;i<enemies.length;i++){
        enemies[i].update();
    }
    for(i=0;i<enemies.length;i++){
        enemies[i].draw();
    }
    requestAnimationFrame(updateArea);
}