The first row of crochet is often the most difficult to work. It can sometimes help to use a larger size hook for the foundation row than you are going to use for the body of the work.
When you have made your row of chains, tip them toward you slightly and you will see that each crochet stitch is made up of three strands: what looks like a row of “V” at the front and a ridge at the back.
The most usual way of working into the foundation chain is to insert the hook from front to back under two strands of the chain, the top leg of the “V” and the ridge from the back.
This leaves one strand from the bottom leg of the “V” for the “cast-on” edge. Occasionally, a pattern instruction will require you to insert the hook under one strand only; this usually means the top strand of the “V” but will sometimes mean the ridge from the back.
Always read the instructions through carefully. If there are no specific instructions, then always insert the hook under the top two stands. After you have made the first crochet stitch into the appropriate chain, insert the hook into every chain along the row and work in your chosen stitch to the end.
If you are working an open or lacy pattern, the instructions may require you to miss a number of crochet chains between each stitch. Count these by counting the number of “V”s along the foundation chain.