While Rust has a relatively early ecosystem of libraries, it is a strong ecosystem for a variety of domains. The main place you find a crate is on, fittingly, crates.io.
After you search for a crate on there, and you want to add it, you can run a simple command. For example, to add the popular serialization/deserialization crate serde, you would run
cargo add serde
This would add the latest version.
If you want to add it manually, you can specify the version in
Cargo.toml with a line like
serde = "1.0.154".
The version you specify is matched with semver. To avoid just repeating the docs, I refer you to the official docs if you want to do something more advanced or want to understand how it's handling version matching.