Single crochet in a chain space--help!

[mollyawesome]

Hi everyone, I hope someone will be able to help me with this!

I'm currently crocheting a ripple afghan, and I can't quite figure out what this means: [sc in ch-1 sp, sc in next st]. I get that there are chain spaces, because in the previous row I do [ch 1, dc in next sc]. But the only online instructions I've found say how to double crochet in a chain space.

What I tried to do was just stick the hook into the space, take one thread, yarn over and pull through the two loops, but it wound up being very lumpy, and on my next row my stitches were definitely off.

Thanks a lot!