What happens if

i use really big needles, and yarn that is too thin? or if I use yarn that is much bigger than the needles, like if i was making an afghan? Idk if that is a dumb question or not, i was just curious.

if you use a yarn that is much thicker than the needles would normally work, it will create a denser fabric. if you try to work with a super bulky yarn and use a really small needle, it can be very difficult to work the yarn. not really impossible but you likely won’t want to do it again for a while.

if you use a really thin yarn on big needles you will have a very lacy effect.

Thin yarn on thick needles will give a fabric so thin it’s really more like net. I did this with a standard boucle wool on 1.5 cm needles (that’s about 3/5 of an inch for you old-fashioned folks) and got a very net-like fabric.
Plus: worked up very fast, I made a blanket in a very short time. Also it was in easy fast garter stitch - good project for that mindless telly-watching - yet my knitter friend said it didn’t look like garter, she had thought it was a lacy pattern, looked very flash.
Minus: wasn’t very warm. Actually, given its nettiness, I’m surprised it had any warmth.

Wool done on thicker-than-recommended needles gives a softer, cuddlier, lighter, floatier, more flexible fabric. Lace paterns are often done on bigger-than-recommended needles.

Wool worked on thinner needles than recommended gives a thicker, denser, stiffer, warmer fabric. Socks are often done on slightly-smaller-than-recommended needles especially to give this sturdier, longer-lasting, warmer fabric.

The label recommends a needle thickness/stitch gauge, this is usually based on what the manufacturer considers to give a nice fabric somewhere in between: warm, but still draping and flowy enough - not too stiff.

If you’re thinking about doing a blanket, may I advise you to choose a pattern that uses fewer stitches on big needles? Blankets can take a LONG time. If your favourite wool for this project is too thin, you can use multiple strands on thicker needles. I’ve seen 2.5 cm needles. That would make a blanket very quickly! You’d need a very thick wool or multiple strands, of course, if it were to work as a blanket.