nützlich
useful
Helpful, advantageous, or well suited and applicable for a particular purpose.
Ein Taschenmesser kann auf einer Wanderung sehr nützlich sein.
A pocketknife can be very useful on a hike.

useful
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useful
Helpful, advantageous, or well suited and applicable for a particular purpose.
Ein Taschenmesser kann auf einer Wanderung sehr nützlich sein.
A pocketknife can be very useful on a hike.

'Nützlich' (useful) belongs to the word family of 'der Nutzen' (benefit, use) and the verb 'nutzen' (to use). Something is 'nützlich' (useful) if you can use it well or if it has a benefit.
Diese App hat viele nützliche Funktionen.
This app has many useful features.
The adjective 'nützlich' (useful) is very often used with the preposition 'für' + accusative to name the purpose or person for whom something is helpful.
Ein gutes Wörterbuch ist sehr nützlich für Deutschlernende.
A good dictionary is very useful for German learners.
Common combinations are 'ein nützlicher Tipp' (a useful tip), 'ein nützliches Werkzeug' (a useful tool), or 'ein nützlicher Hinweis' (a useful piece of information). The expression 'sich nützlich machen' (to make oneself useful) is also common.
Danke, das war ein sehr nützlicher Hinweis!
Thanks, that was a very useful piece of information!
practical / virtually
'praktisch' and 'nützlich' are close in meaning because both say something positive about usefulness. 'nützlich' mainly means that something helps or brings an advantage. 'praktisch' often also means that something is easy to use or requires little effort in everyday life. A tip can be 'nützlich' because it helps. A bag is 'praktisch' if it is well organized and easy to use.

Die Liste mit neuen Wörtern war für die Prüfung sehr nützlich.
The list of new words was very useful for the exam.
Ein Rucksack mit vielen Fächern ist auf Reisen besonders praktisch.
A backpack with many compartments is especially practical when traveling.