Which spindle is best for a beginner?
Well, you don't want something too heavy, because a heavy spindle will tend to pull your fibres apart. And you don't want something too light, because it won't spin for very long. I'd say something between 35g and 45g would be ideal, with a whorl that's not too small, say 2.5" diameter or more.
A brief Physics interlude....heavier spindles will spin for longer than lighter spindles, but more slowly. Larger spindles (in diameter) will spin for longer than smaller spindles, but again more slowly.
What fibre should I use if I'm a beginner?
My personal favourite for an easy spin is Jacob. It's not the softest of fibre and you probably won't want to wear it next to your skin, but it's nice and grabby and your unspun fibre will hold together nicely when you're getting used to drafting the fibre out. Many other undyed fibres will be fine as well: Shetland, Whitefaced Woodland, Cheviot, Manx Loaghtan, or Blue Faced Leicester if you want to spend a little more.
Once you've mastered the easier fibres then you can move on to slippier fibres like Merino, Silk etc.
My other business, Adelaide Walker, has a nice selection of natural fibres.
This video that we made a couple of years ago is a good introduction to preparing fibres for spinning.
So how do I actually spin?
Here's another little video we made....