Add padding between posts and images

You need to do this in your style.css.

Look for

.alignleft {
   float: left;
}

.alignright {
   float: right;
}

and change it to something like this:

.alignleft {
   float: left;
padding: 0 5px 5px 0;
}

.alignright {
   float: right;
padding: 0 0 5px 5px;
}

you can change the padding values. The four values stand for top, right, bottom, left.