Send the visitor to the checkout page of your WooCommerce store
You can use a link to directly add a product to you cart with something like this:
Add Product ID 25 with quantity of 1
https://example.com/?add-to-cart=25&quantity=1
Add Product ID 25 with quantity of 3
https://example.com/?add-to-cart=25&quantity=3
Using this plugin, you simply have to add the gotocheckout=true parameter to redirect to the checkout:
Add Product ID 25 with quantity of 1 and redirect to checkout
https://example.com/?add-to-cart=25&quantity=1&gotocheckout=true