The full Apache 2.0 license text is at /LICENSE in the source tree. Summary:

• You can: use, modify, distribute (commercially included)
• You must: include the license + copyright + state changes you made + retain attribution notices
• You can't: hold the contributors liable, or use the NVTrader name to endorse derivatives without permission

Third-party code in third_party/ retains its own license — don't relicense those.