The simplest and lowest cost solution is to replace the shower head with one designed to increase the pressure.
Mixer valve
Shower faucets are typically made out of linoleum metal. They use this kind of metal because it is resistant to all sorts of soap scum and will not block water flow.
water pressure
The flow of water from the shower creates a low-pressure area inside the shower stall, causing the shower curtain to be drawn inward due to the difference in pressure between the inside and outside of the shower. This phenomenon is called the Bernoulli principle, where higher speed of a fluid (in this case, the water spray) results in lower pressure.
Some causes for a sudden water pressure drop: 1) A big leak on the main supply line. 2) one or more faucets or shower heads opened on the same water line. 3) A utility water pump failure.
Low water pressure or cold water main undersized.
Have you got two single faucets or a single lever faucet? It could be a pressure imbalance or it could just need maintenance
If the pressure problem is in the shower try removing the shower head but leave the shower arm in place. Then turn the water on and see if you have a good flow of water with no shower head in place. Sometimes the shower head gets clogged with a mineral deposit which needs to be disloved with something like CLR (brand name). Some bath faucets have a screen which can be unscrewed and cleaned as well but his is rare. If thhese checks do not help you will probably need a plumber to check if there is anything that can be done such as replacing pipes which may be clogged with deposts.
Many tub/shower valves are designed to be used either as a tub only or as a tub-shower combo. You will note that the valves have inlets on the sides for the hot & cold water supply, and outlets top and bottom for directing water either to the tub or diverted to the shower head. By plugging the bottom outlet with the appropriate plug and either soldering or wrapping the threads with teflon tape, the valve directs the water to the shower head.
If you mean a well tank, the water is forced in by the pump. The residual air pressure pushes the water out to the faucets.
Water droplets and water vapor. Also negative ions.
This does vary slightly according to the shower, but for a shower without a pump, using a gravity feed, a water pressure of at least 0.1 bar is recommended. If your water pressure is low you will need to install a pumped shower.