Launch GTA V. Once you are in the main menu or story mode, "Inject" the menu via the launcher.
If you are looking for a review of its legacy or current alternatives, here is the breakdown: Review Summary: 2Take1 (Legacy) 1 take 2 mod menu
While the features of 1Take and its subsequent updates are impressive, the context in which they are used is vital. Launch GTA V
While it was active, the menu was famous for its "VIP" version and extensive capabilities: Safety & Protections: 1 take 2 mod menu