Are you knitting flat or in the round?
As long as the working yarn is still through the stitch just pick it up and keep knitting. If it's a loose stitch and the working yarn is coming from the next stitch pick up the loose one on the left needle and then knit it.
Even knitters who've been knitting a long time make mistakes and drop stitches so you're not alone. Learning to fix mistakes is part of the process.
We have some videos here for fixing mistakes that will probably help you out at some point.