How do I compile a library into a lib/ folder?

Question

This is my first time using CMake as a developer, and I want to compile some libraries for my project into a lib/ folder.

I'm on Ubuntu 18.04 LTS and running CMake from the command line.

There's 2 libraries I wish to use:

• Magick++
• https://github.com/ljfa-ag/libnbtplusplus

(I'm also using TCLAP but that's implemented entirely in headers.)

I know about and am using the standard folder layout (bin/, build/, include/, src/, etc).

The libraries (especially libnbt++) are specific for this project and I don't want to install them globally. How do I compile them into my lib/ folder?