wahrnehmen
to perceive
To register or notice something with the senses (sight, hearing, touch, smell, taste).
Ich konnte aus der Ferne eine Bewegung im Gebüsch wahrnehmen.
I could perceive a movement in the bushes from a distance.

to perceive / take
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to perceive
To register or notice something with the senses (sight, hearing, touch, smell, taste).
Ich konnte aus der Ferne eine Bewegung im Gebüsch wahrnehmen.
I could perceive a movement in the bushes from a distance.

'Wahrnehmen' (to perceive/take) is a separable verb. In a main clause, the prefix 'wahr' comes at the end. In subordinate clauses or in the infinitive with a modal verb, the verb stays together.
Ich nehme einen seltsamen Geruch wahr.
I perceive a strange smell.
The verb is made up of 'wahr' (true) and 'nehmen' (to take). The literal meaning is 'to accept something as true' or 'to hold something to be true', which explains the idea of sensory perception or noticing well.
Erst nach einigen Sekunden nahm er die Gefahr wahr.
Only after a few seconds did he perceive the danger.
In this meaning, 'wahrnehmen' (to take) is almost always used in fixed combinations. The most important are: 'eine Chance/Gelegenheit wahrnehmen' (to take an opportunity), 'einen Termin wahrnehmen' (to keep/attend an appointment), and 'sein Recht wahrnehmen' (to exercise one's right).
Wenn Sie mit der Entscheidung nicht einverstanden sind, sollten Sie Ihr Widerspruchsrecht wahrnehmen.
If you do not agree with the decision, you should exercise your right to object.
There are also fixed collocations in this meaning, usually referring to official roles. Typical are: 'eine Aufgabe wahrnehmen' (to perform a task), 'eine Funktion wahrnehmen' (to perform a function), or 'seine Verantwortung wahrnehmen' (to fulfill one's responsibility).
Sie nimmt ihre Verantwortung als Teamleiterin sehr ernst wahr.
She fulfills her responsibility as team leader very seriously.
When you want to describe how something is experienced or interpreted, you need the preposition 'als' (as). The structure is always: 'jemanden/etwas als ... wahrnehmen' (to perceive someone/something as ...).
Er nahm die Stille im Haus als unangenehm wahr.
He perceived the silence in the house as unpleasant.
to see
'sehen' and 'wahrnehmen' can both mean that you notice something with your eyes. 'sehen' is the normal everyday word when it is about the eyes. 'wahrnehmen' is somewhat more general: you can see, hear, feel, or smell something. It often emphasizes that you notice something consciously. If you simply mean that your eyes recognize something, 'sehen' sounds more natural. If you want to say that something catches your attention or that several senses may be involved, 'wahrnehmen' fits better.

Maria hat den leisen Geruch von Rauch schon im Flur wahrgenommen.
Maria noticed the faint smell of smoke in the hallway already.
Vom Fenster aus sehe ich den Spielplatz auf der anderen Straßenseite.
From the window, I can see the playground on the other side of the street.