Not stupid at all. Boge are the most popular cartos and great to learn on at 3.0 (won't singe as easily as you learn to keep them damp). I use the 3.0 ones all the time because I share them with my slim manual 510 and slim ecigs should only use standard resistance (what the 3.0 are). I enjoy the 3.0's, especially with the bit of extra heat on the Riva.
You should also buy a 510 atomizer for testing juice since you got the carto kit (best to get 2 atomizers - 2.5 ohms or so would be good). Test juices on the atomizer with a drip tip and also to vape ones that don't earn cartomizers. And put your favorites in cartomizers. Cartomizers are hard to impossible to clean, dry and ever have work well again. So I don't bother. I use a carto with the same or compatible juice until it doesn't work well any more then start a new one. I alternate
vaping a contrasting flavor pair, and usually get 2 weeks out of the pair, often an extra week out of one.
Note - atomizers usually arrive with nasty primer on them like machine oil. * Blow out the atty into a tissue, drip 4 drops of liquid on the bridge /\, wait and let that soak in, vape that mostly off without inhaling. Repeat from * until the vapor tastes ok on an inhale.
---
How I fill a cartomizer (Vapor4Life for KR8 or Boge 510 for 510 which are all soft-cap w/ no inner seals and defined central air channel)
I use thin (20% or less VG) liquid or Vapor4Life WOW liquids, preferably clear liquids w/ no sediment
Filling a blank carto - I pop off the soft cap (unbent paperclip carefully in the mouth hole, not catching any wires or stuffing!). I hold some tissue against the threaded end hole. I tilt the carto and slowly drip 18 drops onto the inner wall of the carto so it slides down into the stuffing while I rotate the carto. Then I wait 15 seconds or so then I drip however many more drops the stuffing wants to soak up. Then I do clean-up. If it is leaking, I clean that up. Then I tilt the open end down into the tissue and puff hard a few times into the threaded end to clear any juice out of the central air channel (I want to see light through there). If it looks too wet above the stuffing, I gently touch a bit of tissue to the stuffing (otherwise that liquid will be gurgling or spitting in my mouth). Then since this was a fresh fill of a blank, I now let it settle. I lay the carto on different sides for 15-20 minutes. Then it should be ready to vape. If you use thicker juices than me, then you may need to let it settle longer.
As I am vaping - if the vapor gets a bit light or a bit dry or tastes bit off or the carto is getting unusually warm, I will take the carto off the battery, open it, add 6-8 drops or whatever it seems to want (I will either hold a bit of tissue against the threaded end hole just in case, or skimp on how many drops I add to make sure I avoid drips if I have no tissue). I check to make sure the threaded end is dry, give it a couple of puffs into the threaded end to make sure the air channel is clear, and continue to vape.
Note - it is easy for me to "open" my main cartos for adding juice because I replace the white end cap with a plastic or delrin drip tip (I get them at LiteCigUSA.net). So I can easily pull that out with my fingers when I add juice and it keeps my lips cool if the carto is hot.