A provisional cast on holds your cast on stitches live so they can be knit later – it allows you to knit in both directions.
This is a very useful technique and I use it a lot to create seamless garments and accessories.
Although there are a lot of ways to provisionally cast on stitches (and I have tried many of them), this one is my favourite:
With a crochet hook, you crochet the stitches directly onto your needle. The crochet chain can later be removed to expose the live stitches.
It’s fast & easy!

Here’s how it works in detail: