As far as end product: it depends. Generally, you can use either to make anything, but knit tends to be better for clothes and crochet tends to be better for things like toys or bags, because it ends up with a stiffer structure.
You can absolutely tell when it's knit vs crochet. If you ever see something crocheted in a store, someone handmade that; machines can't do an actual crochet stitch. Knitting uses the needles to create rows of interconnected stitches, usually resulting in V-shaped patterns, while crochet uses the hook to create loops, which almost look like knots at the end. Knitting is functionally two stitches (knit and purl) that are used to create different patterns, while there are five basic crochet stitches that form the base of ~150 different potential stitches. I think I know about 10 crochet stitches.