It's written in Rust.
Typically, you install Rust using rustup.
Run cargo doc --open to build and open the documentation in a browser.
Before committing/pushing, make sure to run ./check.sh, which runs
all the tests and lints that Travis will.
Running cargo tests will run the tests.
There are a couple interesting tests in the tests directory:
prop.rs implements propositional logic and proves some simple
theorems.math.rs implements real arithmetic, with rewrite rules and a test
case taken from Herbie.