pflegen
to care for
To look after and provide care for a person who is sick, old, or in need of help.
Die Krankenschwester pflegt die Patienten auf der Intensivstation.
The nurse cares for the patients in the intensive care unit.

to care for / maintain
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to care for
To look after and provide care for a person who is sick, old, or in need of help.
Die Krankenschwester pflegt die Patienten auf der Intensivstation.
The nurse cares for the patients in the intensive care unit.

The verb 'pflegen' (to care for / maintain) is the basis for the noun 'die Pflege' (care; e.g., elderly care, nursing care) and the adjective/participle 'gepflegt' (well-kept; e.g., a well-kept garden, a well-groomed appearance).
Die Pflege von kranken Menschen ist eine anspruchsvolle Aufgabe.
Caring for sick people is a demanding task.
The meaning of 'pflegen' (to care for / maintain) becomes clear from the object: if it refers to a person, it is about care. If it refers to a thing or a relationship, it is about maintenance. If 'zu' with an infinitive follows, it describes a habit.
Er pflegt seine kranke Mutter zu Hause.
He cares for his sick mother at home.
In the meaning 'to keep in good condition', 'pflegen' (to maintain) is often used for abstract things. Typical collocations are 'Kontakte pflegen' (to maintain contacts), 'Freundschaften pflegen' (to maintain friendships), 'eine Tradition pflegen' (to maintain a tradition), or 'sein Image pflegen' (to maintain one's image).
Es ist wichtig, berufliche Kontakte zu pflegen.
It is important to maintain professional contacts.
In this formal meaning, 'pflegen' (to be in the habit of) works similarly to a modal verb. It is used with 'zu' and an infinitive at the end of the sentence. The subject is the person who has the habit.
Mein Großvater pflegte zu sagen, dass Geduld eine Tugend sei.
My grandfather used to say that patience was a virtue.
to receive / preserve / support
'erhalten' and 'pflegen' are closely related when something is meant to stay in good condition. 'erhalten' describes more the goal or result: something continues to exist and does not fall into decay. 'pflegen' describes more the regular work needed for that, for example cleaning, watering, repairing, or taking care of something. You can 'einen Garten pflegen' (maintain a garden) in order to 'ihn zu erhalten' (preserve it). Learners may confuse the words because both occur with plants, objects, or relationships. Memory tip: 'pflegen' is the action; 'erhalten' is often the goal.

Im Sommer pflegt Ali die Pflanzen auf dem Balkon jeden Abend.
In summer, Ali takes care of the plants on the balcony every evening.
Regelmäßige Reparaturen erhalten die alte Maschine in gutem Zustand.
Regular repairs keep the old machine in good condition.