Create Configurable Products in Magento

I have simple products already created that I would like put into configurable
For example
https://www.precisiontools.com/wire-shelf-trucks/freezer-wire-shelf-trucks/3-tier-freezer-mobile-units.html

I would want these items to become 1 configurable where the customer will be able to choose via shelf size, unit height and unit capacity.

The end product would look similar to this
https://www.precisiontools.com/chrome-stationary-security-cages.html

I will have you do this one product and if