To delete items you do not want anymore select the checkbox above the recycle bins and press the "DELETE" button. To review your items as thumbnails click the "View Thumbs" link at the top in the NAME / ID column. To continue adding items you can either use the Category Menu on the left of the page or the "Continue browsing at the current CATEGORY" near the bottom of the page. The link at the bottom will take you back to the previous thumbnail page you were on.
When you are done adding items to your shopping cart you can click the "PROCEED TO CHECKOUT" button to go to the Details form.