Error installing a crate via cargo: specified pack

I'm trying to install a Rust crate on my system (Arch Linux) using Cargo. I can search for crates and find what I need, for example:

 $ cargo search curl | head -n3
    Updating registry `https://github.com/rust-lang/crates.io-index`
curl (0.3.0)             Rust bindings to libcurl for making HTTP requests
curl-sys (0.2.0)         Native bindings to the libcurl library

When I try to install it, I get the following error:

 $ cargo install curl
    Updating registry `https://github.com/rust-lang/crates.io-index`
error: specified package has no binaries

What does this mean? Do I have to build it from source first? What's the point of Cargo if it does not install it in the first place?

 $ uname -a
Linux 4.6.1-2-ARCH #1 SMP PREEMPT Thu Jun 2 15:46:17 CEST 2016 x86_64 GNU/Linux
 $ rustc --version
rustc 1.9.0
 $ cargo --version
cargo 0.10.0 (10ddd7d 2016-04-08)

cargo install is used to install binary packages that happen to be distributed through crates.io.

If you want to use a crate as a dependency, add it to your Cargo.toml.

Read the Rust getting started guide and the Cargo getting started guide for further information. In short:

cargo new my_project
cd my_project
echo 'curl = "0.3.0"' > Cargo.toml

Amusingly, you can install a third-party Cargo subcommand called cargo-edit using cargo install that makes it easier to modify your Cargo.toml file to add dependencies!

cargo install cargo-edit
cargo add curl

An important thing to note is that every Cargo project manages and compiles a separate set of dependencies (some background info). Thus it doesn't make sense to install a compiled library. The source code for each version of a library will be cached locally, avoiding downloading it multiple times.