die Öffnung
opening
A hole, gap, or opening in an otherwise closed surface that allows passage through or a view in.
Die Katze schlüpfte durch eine kleine Öffnung im Zaun.
The cat slipped through a small opening in the fence.

opening
Loading your saved state.
opening
A hole, gap, or opening in an otherwise closed surface that allows passage through or a view in.
Die Katze schlüpfte durch eine kleine Öffnung im Zaun.
The cat slipped through a small opening in the fence.

The noun 'die Öffnung' (opening) is directly derived from the verb 'öffnen' (to open). The ending '-ung' turns a verb into a feminine noun that describes the action or the result of that action.
Das Öffnen der alten Truhe war sehr schwierig.
Opening the old chest was very difficult.
When a physical gap is meant, 'Öffnung' (opening) is often described with adjectives such as 'klein' (small), 'groß' (large), or 'schmal' (narrow). Verbs of passage such as 'kriechen' (to crawl), 'schauen' (to look), or 'passen' (to fit) are also typical.
Wir fanden eine schmale Öffnung in der Felswand.
We found a narrow opening in the rock face.
The act of opening is often connected to words that describe an event. Watch for terms like 'feierlich' (ceremonial), 'offiziell' (official), 'während' (during), or 'nach der Öffnung' (after the opening) to recognize this meaning.
Die offizielle Öffnung der Brücke wird vom Bürgermeister vorgenommen.
The official opening of the bridge will be carried out by the mayor.
In connection with the times when a shop or institution is accessible, the compound word 'die Öffnungszeiten' (opening hours) is almost always used in the plural.
Können Sie mir bitte die Öffnungszeiten des Schwimmbads sagen?
Could you please tell me the opening hours of the swimming pool?
The meaning 'Liberalisierung' (liberalization/opening) is used almost exclusively in political or economic texts. Signal words here are 'wirtschaftlich' (economic), 'politisch' (political), or 'des Marktes' (of the market).
Die politische Öffnung des Landes führte zu mehr Demokratie.
The political opening of the country led to more democracy.
beginning
'der Beginn' and 'die Öffnung' can both have to do with the start of a period of time. 'der Beginn' is general and means the beginning of an event or process. In this context, 'die Öffnung' means the time from which a shop, public office, or institution is accessible. So you say 'Beginn der Veranstaltung' (start of the event), but 'Öffnung des Museums' (opening of the museum) or 'Öffnung der Türen' (opening of the doors). 'Öffnung' only fits when something opens for visitors or customers.

Vor der Öffnung der Behörde warten schon mehrere Menschen vor der Tür.
Before the public office opens, several people are already waiting outside the door.
Am Beginn des Arbeitstags liest Clara zuerst ihre E-Mails.
At the beginning of the workday, Clara first reads her emails.