I have installed Audacity 2.2.1 and I’m using Windows 10.

Can somebody help me to generate a noise and then fluctuate its pitch or volume at 4 times each second to create a 4 Hz tone?

I need it for meditation purposes but I know nothing about how to create tones.

Thank you!

Generate → Noise (Maybe try Pink Noise)
Effect → Tremolo (Modulates volume)

Modulating noise will not create a “tone”, but it will give you slowly pulsating noise (a bit like waves on a seashore).

“Noise” does not have “pitch” as such, but a “sweep filter” can give a general sense of rising and falling pitch.

Pulsating noise at 4Hz may not be very relaxing - it will probably sound like a steam train going slowly.

There’s an effect here that produces modulated noise, but the maximum frequency of the pulsation is 1 Hz:
See the description on that page for how to use it.
Instructions for downloading and installing are here: Missing features - Audacity Support

Here’s a plug-in that can generate up to 10 hours, 59 min and 59 seconds of amplitude modulated noise.
It also has a filter that can soften the harshness of the noise.
modnoise.ny (1.03 KB)
Instructions for installing are here: