Learning to knit involves mastering a combination of techniques, from casting on to binding off and everything in between. In order to knit a blanket, however, you do not need to master every knitting technique; knowing how to do a simple, straight knit stitch is enough to knit your way to a blanket.
Choose your materials. When you knit, the larger the needles you use, the larger your stitches will be. The same is true for the yarn you use in your patterns; thicker yarn makes larger stitches and thinner yarn makes smaller stitches. To make a blanket, you can use any combination of yarn and needles; however, it will take a lot less time to knit if you use a chunky yarn and large -- US size 15 or larger -- needles.
You will probably need circular knitting needles to make a blanket. Small circular needles with a connecting cable of 30 to 36 inches are adequate for a baby blanket, but you will want a longer connecting cord for making an adult-sized blanket.
Create a gauge swatch with your choice of yarn and needles. To do this, cast on enough stitches to create a 6-inch-wide swatch, then continue knitting until the swatch is 6 inches long.
Lay the swatch flat and measure across its center with a ruler; count how many stitches and rows are in one square inch of the swatch. Multiply the number of stitches per inch by how many inches wide you'd like your finished blanket to be; the resulting number is how many stitches you need to cast on. So if you want a baby blanket to be 36 inches across and your gauge is 4 stitches per inch -- common with a bulky-weight yarn -- you'd need to cast on 36 x 4 = 144 stitches.
Cast on the determined number of stitches. Knit across the entire row, then turn your work and knit back. Continue until the blanket reaches its desired length.
Bind off the last row of stitches, cut the yarn, and weave in the loose ends using a large-eye blunt needle.