Rockets consist of several stages. Two or more smaller rockets are combined into a single rocket. They are ignited in order; when an earlier stage runs out of propellants, it is jettisoned to reduce the load for the rest of the rocket.
Flat-Earthers noticed videos of rockets being recovered from the ocean and use them as “evidence” rockets never went to space. In reality, these are the jettisoned earlier stages of the rockets. The latter stages do reach space.
Rockets are designed in multiple stages to reduce their energy requirements. Without staging, an empty rocket body that has run out of propellant only becomes a load without having a value to the rest of the rocket. With staging, these mostly empty rocket bodies can be jettisoned, and the latter stages no longer need to deal with the weight of the earlier stages.
The jettisoned earlier stages are either discarded or land to be reused in future launches.
- Multistage rocket – Wikipedia