how to put an img under a header(div) that contains other divs?

I put a header which contains three divs. One has an image and the other two contain text.I then tried putting an image under it which has the same width of the header. But when I first put it, it was over the header div( I thought it should go under it). I then tried pushing it down by increasing the top margin and it worked. But as I increase the width of it the text in the header moves although it is not touching it!

This is the html code:

    <div id="header">
        <img id="logo" src="....">   <!---the logo at the top right--> 
        <div id="name">JANE DOETTE<div>  <!---the text that moves - top left -->
        <div id="job">Front-End Ninja</div>  <!--under the text that moves but doesn't move--->
    </div>

    <img id="image" src="....">  <!---the image-->

This is the css code:

#header {
    height: 6em;
    width:80%;
    background-color: white;
    margin-left:10%;
    margin-right:10%;
    border-bottom:2px solid #BCBBBB;
    margin-bottom:10px;
}

#image{
    margin-left:10%;
    margin-right:10%;
    height:10em;
    width:80%;
}

#logo {
    height:88px;
    width:89px;
}

#name {
    color: #BCBBBB;
    text-align:left;
    float:right;
    font-size:2.7em;
    font-family:sans-serif;
    height:50%;
}

#job {
    color: #BCBBBB;
    text-align:left;
    float:right;
    font-size:0.5em;
    font-family:sans-serif;
    font-weight:bold;
    margin-top:0.2em;
}

Those are my questions:

1. 
   

   Why doesn't the image automatically go under the header div?

   
   


2. 
   

   Why does the text move?

   
   


3. 
   

   Why is the top text the one that moved although the one at the bottom is nearer to the image?

   
   


4. 
   

   What should I do to get the image under the heading div?

   
   


5. 
   

   I adjusted the width of the image to 80%. But it seems to be just 20%. Why?

   
   


6. 
   

   Has it got anything to do with position or display?

   
   

***Sorry for not adding an image of it but I don't have a reputation of more than 10 ( I am not allowed to).

***Sorry for the long questions.( I am still a beginner).

***Your answers would be much appreciated.