If you are familiar with jQuery and Sizzle syntax, d3 selections should not be much different. d3 mimics the W3C Selectors API to make interacting with elements easier.
For a basic example, to select all
<p> and add a change to each of them:
d3.selectAll('p') .attr('class','textClass') .style('color', 'white');
In a nutshell this is relatively the same as doing in jQuery
$('p') .attr('class','textClass') .css('color, 'white')
Generally you will start with a single select to your container div to add an SVG element which will be assigned to a variable (most commonly called svg).
var svg = d3.select('#divID').append('svg');
From here we can call on
svg to do our sub-selections of multiple objects (even if they don't yet exist).