I’m not trying to put you off knitting I the round. If you’re not ready for this or it doesn’t suit you then you can knit flat and seam. Many patterns can be changed to knit flat. There are some video tutorials on this and also help here. I am not an expert at changing a pattern from in the round to knit flat but I’ve done it with sweater sleeves and there are others here who can help too.
For me personally I am fine with a neck edge in the round but can’t manage a small diameter such as gloves, socks or sleeves. I don’t find it a comfortable challenge whereas i enjoy other challenges.
A very simple wrist warmer could be a rectangle (rib with a single pattern column running up the centre) seamed up as salmonmac described. Rib such as 2 x 2 is very forgiving on size, it pulls in to about half the width of stockinette so exact sizing is less important. Cast on and bind off methods become more important so they are not too tight.
If you have yarn remaining after this you might consider a matching head band (wide and worn like a hat but easier to make).
The scarf and wrist warmers will be a great gift set.