stecken
to stick
To put something into an opening or hollow space so that it stays fixed there.
Er steckte den Brief in den Umschlag.
He stuck the letter into the envelope.

to stick / to be stuck
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to stick
To put something into an opening or hollow space so that it stays fixed there.
Er steckte den Brief in den Umschlag.
He stuck the letter into the envelope.

Although 'stecken' (to stick / to be stuck) often describes a state or position, the perfect tense is always formed with 'haben', never with 'sein'.
Der Schlüssel hat die ganze Zeit in der Tür gesteckt.
The key was in the door the whole time.
When 'stecken' (to stick) describes movement (putting something in), it is followed by a preposition with the accusative. When it describes a location (being somewhere), it is followed by a preposition with the dative.
Sie steckt den Stecker in die Steckdose.
She plugs the plug into the socket.
The question 'Wo steckst du?' or 'Wo hast du gesteckt?' is a very common, colloquial way to ask where someone is or was.
Hallo? Ich warte schon seit 20 Minuten. Wo steckst du denn?
Hello? I've been waiting for 20 minutes. Where are you?
To express that you are in a (often difficult) situation, 'stecken' (to be stuck) is frequently used with 'in' + dative. Typical phrases are 'in Schwierigkeiten stecken' (to be in trouble), 'im Stau stecken' (to be stuck in traffic), or 'in der Klemme stecken' (to be in a tight spot).
Ruf mich später an, ich stecke gerade in einer Besprechung.
Call me later; I'm in a meeting right now.
When you secretly give someone something, the verb follows the pattern 'jemandem (dative) etwas (accusative) stecken' (to slip someone something). The person is the dative object, and the thing is the accusative object.
Ihre Großmutter hat ihr zum Abschied heimlich etwas Geld gesteckt.
Her grandmother secretly slipped her some money as she was leaving.
In the meaning 'die Ursache sein' (to be the cause), 'stecken' (to be behind something) is always used with the preposition 'hinter' and the dative.
Ich wüsste gern, wer hinter dieser ganzen Sache steckt.
I'd like to know who is behind this whole thing.
to do
'tun' and 'stecken' can both mean that you put something somewhere. 'tun' is very general and only says that something goes to a place. 'stecken' is more precise: you put something into an opening, pocket, or narrow space so that it is inside there or fits firmly. That is why you cannot use 'stecken' for every place. Learners may confuse the words because people often say 'etwas in die Tasche tun' (to put something in the bag) or 'etwas in die Tasche stecken' (to stick something in the bag). 'stecken' fits especially well with pockets, holes, keys, or cards.

Vor der Fahrt steckt Max den Schlüssel in die Jackentasche.
Before the trip, Max puts the key in his jacket pocket.
Sie tut die alten Fotos in eine kleine Kiste.
She puts the old photos in a small box.