In order for your project to be the same size as the pattern you're following, you should be knitting at a tension where 14 inches and 18 rows is equal to 3 inches. If your stitches are larger or smaller than the designer's stitches, your project will not be the same size.
Knit up a 4 inch by 4 inch swatch using the yarn and needles you plan to use for the project. Then measure your stitches over three inches. If you have fewer than 14, you'll need to use a smaller needle. If you have more than 14, you'll need to use a larger needle.
If you're making a scarf or blanket, gauge doesn't matter as much as if you're making a garment where you have to worry about fit.
Don't worry about row gauge as much, because that can be adjusted by knitting more/fewer rows. The stitch gauge is the important one.
As for the increase 5 stitches evenly, they just want you to increase 5 stitches in that row, evenly spaced (approximately) so you end up with 72 stitches.