Kegging home brewed beer was really how I got started in the home brew business so it’s something I have a special affinity with. To a person starting to keg there seems to be a hundred questions to be answered. They in time, see that there is a perfectly logical reason for things that may seem confusing.

It is simple, because there is a science and therefore logic behind everything.

Firstly, beer will readily accept gas as it chills and release gas, as it warms or is agitated.
Secondly, in kegging many things relate to the first point.

To expand on the first point.

Once you have kegged your beer without oxidising it (used a transfer tube) and you have purged out any regular air with CO2 we can proceed with a gassing procedure.

The keg should if possible, be put into the fridge as any food not sterile can spoil if left unchilled. Beer improves as it is stored cold (lagered).

A simple 260 kpa for 48 hrs and then set at pouring pressure, will put enough gas into the beer for it to be served chilled. This system is the easiest for homebrewers.

Other gassing procedures usually have drawbacks through inconvenience, time taken or in the presentation of the beer.
Pouring the beer through an unchilled tap will cause gas to be released from the beer throwing a big head with flattish beer under it. This is a good reason for the homebrewer to choose a pluto gun, that stays cold inside the fridge. The beer taps at the local pub are cold. A warm glass can have a similar effect to a warm tap.

Pouring overgassed beer will have a similar effect (big head and flat) because the beer will release gas as it is forced through the spear and fittings on the keg. This is similar to turning a bottle of softdrink up side down and just opening the lid a little, (the agitation of being forced through the tiny opening, releases gas). If you have bubbles in your beer line as it is pouring, it is probably overgassed for the pouring pressure and or the system you are using and is releasing gas.

As the level of beer drops in the keg it is important to ensure there is a reasonable pressure left on the beer or it will go flat. This is similar to the 2 litre bottle of softdrink left half empty for a day or two. Likewise, if beer is too gassy, turn off the gas and over a few hours, release pressure through the air relief valve until it pours OK. at pouring pressure.