Look, you dont need to be an engineer to get those shots, but you definitely need a better lens than the kit zoom that came with the camera. In my experience, that cheap zoom is exactly why your photos look flat. You need a prime lens. It doesnt zoom, but it has a much larger aperture. Since you are using a D3500, you have to be very careful... that camera body lacks an internal focus motor. If you buy an older AF-D lens, it wont autofocus and youll be miserable trying to focus by hand during a ceremony. I highly recommend the Nikon AF-S DX NIKKOR 35mm f/1.8G. I have owned several over the years and it is basically the gold standard for budget DX shooters. You can usually find them used for about $110 online. The f/1.8 spec is the magic part. It lets in a ton of light and creates that shallow depth of field you are looking for. Just set your camera dial to A and roll the thumb wheel until it says 1.8. If you want even tighter shots, look for a used Nikon AF-S NIKKOR 50mm f/1.8G. It is fantastic for headshots, though it can feel a bit cramped for indoor group photos. Used copies are usually right around $140. Honestly, the 35mm is more versatile for a wedding. It gives you that pro look without forcing you to stand 15 feet away from everyone just to get them in the frame...