How can Arduino send an RF signal at 433 MHz?
The short answer: It doesn't.
Arduino doesn't send anything close to that high. It can only send a lower frequency (lower bitrate) signal over a 433MHz CARRIER frequency (or any other frequency for that matter) by using another device/module which generates a very high frequency (radio frequency) in order to communicate via radio waves.
The 433MHz in this case is NOT THE RATE OF DATA/BITS, but a frequency of the radio signal over which the data is transmitted/received.
Your question shows a lack of knowledge about the meaning of, and the difference between, processor clock frequencies, speed of processing, data rate, and "carrier" frequencies as the means of radio communication, so you should read and learn more about basic computer processing and its related terms, and about the means and ways of transmitting information over radio waves.
Basically, the carrier/radio frequency is modulated/changed by the information/data you want to transmit, so it is those changes that represent the information.
Based on the type of change, there 3 basic types of modulation.
Amplitude Modulation (AM), Frequency Modulation (FM), Phase Modulation (PM).
With AM, the carrier frequency is kept stable/same, while the amplitude/power of the carrier frequency is varied to transmit information.
FM keeps the carrier amplitude the same (at maximum) while the frequency changes up and down a certain amount represent information.
PM is similar to FM, and it carries information by phase-shifting the carrier frequency.
Why is it that when I google the frequency of arduino uno it says:
16 MHz is the clock frequency of the processor, basically how fast the CPU core runs.
If that is true then how can an Arduino send a 433 MHz frequency?
You would buy a radio that transmits at 433 MHz center frequency. The speed of the CPU has no relationship to what frequency the radio transmits at. For example, in the extreme case of a fiber optic, the optical frequency is 300,000 GHz, but your CPU would still be 16 MHz.
When I set now delay on Example 3 the highest frequency I could obtain was 112 kHz (with a k). How is it possible to send a 433 MHz frequency (with an M)?
The radio datasheet should give you an idea of how to connect to it, but basically it would attach over some bus (e.g. USB) or provide you with some data signal that you would read in. What does the radio's datasheet say to do?
These "examples" seem to be questions that can be answered:
3) Toggling a pin in a loop with DigitalWrite function is slow. That is why you only get 112 kHz. The microcontroller still runs with 16 MHz clock.
4) The transmitter generates its own RF carrier wave. You can send slow data for the module to transmit.