filmen
to film
To record moving images with a camera in order to create a film.
Sie hat den gesamten Urlaub mit ihrem neuen Smartphone gefilmt.
She filmed the entire vacation with her new smartphone.

to film
Loading your saved state.
to film
To record moving images with a camera in order to create a film.
Sie hat den gesamten Urlaub mit ihrem neuen Smartphone gefilmt.
She filmed the entire vacation with her new smartphone.

The verb 'filmen' (to film) is derived directly from the noun 'der Film' (the film/movie). This structure, in which a noun becomes a verb, is very common in German.
Für ihr Schulprojekt will sie einen kurzen Film drehen und alles selbst filmen.
For her school project, she wants to shoot a short film and film everything herself.
'Filmen' is a transitive verb and almost always needs an accusative object. You ask: Wen oder was filmst du? (Whom or what are you filming?)
Der Tourist filmte die beeindruckende Architektur der alten Kirche.
The tourist filmed the impressive architecture of the old church.
'Filmen' is often used with a preposition that describes the device, for example 'mit dem Handy filmen' (to film with a mobile phone) or 'mit einer Drohne filmen' (to film with a drone).
Er filmt seine Reisen immer mit einer professionellen Kamera.
He always films his travels with a professional camera.
to record / take in
'aufnehmen' and 'filmen' can both mean that you save images with a device. However, 'filmen' only fits moving images with a camera, that is, videos or films. 'aufnehmen' is broader: you can record a video, but also music, a conversation, or sounds. Learners may confuse the words because with videos you can often say both. When it is clearly about a camera and moving images, 'filmen' often sounds more precise. When it is generally about recording sound or images, 'aufnehmen' fits better.

Beim Training filmt du die Übung, damit du sie später noch einmal ansehen kannst.
During training, you film the exercise so you can watch it again later.
Yusuf nimmt das Lied mit seinem Handy auf.
Yusuf records the song with his phone.