Holding patterns must be used when, due to high traffic volumes or bad weather conditions a landing permit cannot be issued by the ATC.
A Holding resembles an oval race track, whose fixed point (Holding Point) is usually based on a VOR or NDB station.
The straight lines of the holding are the approach (inbound) and the departure (outbound).
The curves at the fix end or outbound end are standard curves (max. bankangle 20 - 25 degrees).
Standard holdings are always flown in right turns.
But of course there are exceptions here as well, i.e. the Holding is then flown with left turns.
Holdings near the airport are arranged in such a way that each ILS can be approached directly from them and usually can be intercepted with an angle of at least 30 degrees.

Holding loops near the airport are flown in the lower area, i.e. below FL 140 to 8000ft.
These usually include approach routes, so that holdings are not usually flown here.
Altitudes for holdings in the approach charts are always to be understood as minimum flight altitudes.
The speed in the holding for our aircraft (A320, 737/757/767 ) is usually 230 kts below FL 140, unless ATC says otherwise.
In the Holding all must fly at the same speed. Above FL 140 up to and including FL 200, flying is at 240 kts. Above FL 340 to FL 340 with 265 kts.
The flight time of the inbound or outbound legs is below FL 140 at one minute. Above FL 140 at 1 min. 30 sec.
Time measurement using the stopwatch does not start until the curve is completed.

The most difficult thing about a holding is the entry. The starting point of a holding is always the fixed point.
The decisive factor here is the course you take towards the fixed point of the waiting loop.
Three different sectors are distinguished here. Depending on which of the three sectors I am using Fixed point closer decides about the entry maneuver.

Direct entry: (180° sector)

Here you approach the holding fix from the so-called 180° sector.
After flying over the fixed point, the holding is started with a standard curve.

Parallel entry: (110° sector)

Here you approach the holding fix from the so-called 110° sector.
After flying over the fixed point you are outside the holding.
One then flies parallel to the approach course for one minute, then in the direction of the holding loop (left at standard holding) and captured the inbound rate at the fix.
After flying over the fix, the actual wait loop begins.

Teardrop entry: (70° sector)

Here you approach the holding fix from the so-called 70° sector.
After flying over the fixed point, you are in the holding loop and on the opposite course to the approach section. After the fixed point has been flown over, one flies a course that is 30° lower than the course of the departure section (outbound), e.g. outbound target rate 90°, results in a rate to be flown of 60°.
This course is then held for one minute. With the standard holding, after the time with standard curve turned to the right and captured the radial of the approach course to the fixed point.
After flying over the fix, the actual wait loop begins.