Question for anyone that got 3D ultrasound

Marisssa 🌙 • PME 07•04•16 👧🏼💜 | SSE 03•31•18 👶🏼💙 Traveler. | Lover. | FreeSpirit. | In Love.
Going to be setting up an appointment for a 3D ultrasound and was wondering how it happens? Like how exactly do they do it? I know I could google but it'll be easier to know from other people's experiences!!! Please tell. :)