basteln
to craft
To make creative things as a hobby from various materials such as paper, wood, or fabric.
Zu Ostern basteln wir mit den Kindern bunte Nester.
At Easter, we craft colorful nests with the children.

to craft / tinker
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to craft
To make creative things as a hobby from various materials such as paper, wood, or fabric.
Zu Ostern basteln wir mit den Kindern bunte Nester.
At Easter, we craft colorful nests with the children.

Nouns are also derived from the verb 'basteln' (to craft/tinker). 'Der Bastler' (the hobbyist/tinkerer) is the person who crafts or tinkers, and 'die Bastelei' describes the activity or the result of crafting.
Mein Onkel ist ein leidenschaftlicher Bastler und repariert alles selbst.
My uncle is a passionate tinkerer and repairs everything himself.
When you work on a device or project, 'basteln' (to tinker) is always used with the preposition 'an' and the dative. This structure shows that you are working intensively on something in order to improve or repair it.
Der Informatiker bastelt an einer neuen App.
The software developer is tinkering with a new app.
In the creative sense, 'basteln' (to craft) is often connected with the materials or the occasion. Typical phrases are 'aus Papier basteln' (to craft with paper), 'mit Holz basteln' (to craft with wood), or 'Weihnachtsschmuck basteln' (to make Christmas decorations).
Für den Geburtstag meiner Freundin bastle ich eine persönliche Karte.
For my friend's birthday, I am making a personal card.
The preposition 'an' is a clear signal that 'basteln' is meant in the sense of 'tüfteln' (to tinker) or 'improvisiert reparieren' (to repair in an improvised way). Without this preposition, it is usually about creative crafting as a hobby.
Er bastelt an seinem Fahrrad, um es wieder fahrtüchtig zu machen.
He is tinkering with his bicycle to make it roadworthy again.
to build
'bauen' and 'basteln' can both mean that you make something with your hands. 'bauen' is more suited to solid, larger, or planned constructions, for example a house, a shelf, or a model. 'basteln' is often used for creative work as a hobby, especially with paper, wood, or small materials. It can also mean that you work on something and improvise. Learners may confuse the words because with both you are making something. However, 'bauen' usually sounds more serious and stable, while 'basteln' sounds smaller, more creative, or more makeshift.

Bei schlechtem Wetter bastelt Erik aus Karton ein Geschenk für seine Schwester.
In bad weather, Erik makes a gift for his sister out of cardboard.
Im Garten bauen die Eltern ein kleines Haus für die Kinder.
In the garden, the parents are building a small house for the children.