You have installed the VirtueMart component and can add products to the cart - but you cannot see the cart and have no link to checkout.
If so, you need to publish either the minicart in the main VirtueMart module, mod_virtuemart, or publish the VirtueMart minicart module, mod_virtuemart_cart. All accomplished through Joomla's module manager.
If you do not see the modules in Joomla's module list then you should install them. They are in the modules directory of the VirtueMart Complete Package.