The bag icon at the top right corner of the page is your cart. The number will tell you how many items are in the cart.
From here, you can edit quantities of the items in your cart by clicking the bag and pressing the + or - buttons, or by replacing the quantity number.
If you want to remove an item completely, change the item quantity to 0 or click "Empty Cart".
If you decide that you want to checkout, the "Checkout" button below your items.