Open Poser 12.

Click File, scroll down to Install Zip File.

Choose file.

Choose which runtime you want it in. I suggest  selecting the one called 'Download' from the menu by dropdown. That library is created for you. If you want to create one on an external drive, do it before you start any install. Just make a folder, call it what you like.

Click Install.

Do this for each Zip file.