To start a new project with Foundry, use forge init:

$ forge init hello_foundry

This creates a new directory hello_foundry from the default template. This also initializes a new git repository.

Move into your newly created project:

cd hello_foundry

Let's check what the default template looks like:

$ tree . -d -L 1
.
├── lib
├── script
├── src
└── test
 
5 directories

The default template comes with one dependency installed: Forge Standard Library. This is the preferred testing library used for Foundry projects. Additionally, the template also comes with an empty starter contract and a simple test.

Compile your contracts:

$ forge build
Compiling 23 files with Solc 0.8.30
Solc 0.8.30 finished in 353.18ms
Compiler run successful!

Execute the test suite:

$ forge test
No files changed, compilation skipped
 
Ran 2 tests for test/Counter.t.sol:CounterTest
[PASS] testFuzz_SetNumber(uint256) (runs: 256, μ: 31965, ~: 32354)
[PASS] test_Increment() (gas: 31851)
Suite result: ok. 2 passed; 0 failed; 0 skipped; finished in 6.19ms (4.81ms CPU time)
 
Ran 1 test suite in 105.48ms (6.19ms CPU time): 2 tests passed, 0 failed, 0 skipped (2 total tests)

You'll notice that two new directories have popped up: out and cache.

The out directory contains your contract artifact, such as the ABI, while the cache is used by forge to only recompile what is necessary.