Hi Rrrrronan,
Perhaps, checkout these tutorials which should help guide you to getting to what you are trying to achieve. You can find a lot of other similar info/tutorials if these aren’t suitable.
If you want the “background” portion of your render to be transparent then remember to switch on “Transparent” from Properties Panel > Render > Film > Transparent section. Your objects will still be visible but just the background will be transparent like in my example below.
Alternatively, if your image (with an alpha channel) is used as a material then we can take advantage of the alpha portion to make your object partially transparent. See the node setup in my example (which should work in both Eevee & Cycles). For Eevee though remember to set the Render > Shadows settings and Material settings correctly (see https://www.katsbits.com/codex/transparent-shadows/) otherwise it will not work as expected. You’ll note that with the transparent alpha blended objects these will also appear as expected on your transparent background. Hope this helps.
Cheers and happy blending!