Float images in content

You need to setup CSS settings for alignleft class of your theme:

.alignleft, img.alignleft {
    /* ... */
    display: inline;
    float: left;
    /* ... */
}

And you need to add editor stylesheet where the same CSS will be presented. Create editor-style.css file in your theme, put content CSS settings there and call add_editor_style(); from you functions.php file.