Prepping containers for gardening is not a major secret at all. All you have to do now is to go to YouTube and look up videos on how to prepare what ever kind of container you are going tp use in your garden. Ultimately all the containers you use will need proper drainage to keep your soil from becoming completely swampy, stagnant, and water-logged.
Once you found the container you want to use this is where the fun begins.
Grab a drill and drill holes in the bottom of the container. I drill nine holes on average per container. I put five holes in the inner part of the bottom of the container and one hole in each corner for a total of nine holes. Hole placement is entirely up to you because only you know what you want drainage wise for each container.
Flip the container over and put what ever medium you want at the bottom of the container to create at least an inch or two of space to allow drainage. In some of the containers I have, I used gravel rocks. But as of late I have also been using Bamboo really dead bamboo as you see in the picture below.
The reason I chose the bamboo was for 2 reasons, the first one was to create good drainage and second reason was to allow the dead bamboo to breakdown and put nutrients back into the soil. Bamboo is considered a weed so if you plan to use bamboo make sure it is dead.
You pour the soil in the container that you have ready with amendments.
Let all the contents in the container settle for a few days. If there is rain in the forecast in the next 2 or 3 days, wait for the rain to water the container. If not water the container then let it sit untill you know what plants you are gonna put in that particular container.
Once all that is done then you have a container that is ready to be populated with plants.