There are lots of ways to make one, (m1) your pattern suggest a M1 purl wise.
(Again, lots of ways!)
ONE common way to make 1 is to lift the yarn between a just knit, and an about to be knit stitch.
you lift and 'twist' the bar into a stitch.
twist it one way, its a Knit wise, twist it the other way, its is purl wise. (the difference is subtle!)
EZ (elizabeth zimmerman) used a different make 1, (than the way that is commonly recommonded today!)
she make a simple (script letter e) cast on between 2 stitches.
the E can be front facing (knitwise) or backwards (think of the schwa!) (purl wise).
a YO is an other sort of make 1, (but usually not subbed for a make 1, since a YO leaved a definate hole. (and make 1's, are in general invisible!)
KFB (knit in front and back of a stitch) or Kand purl into a single stitch are not as noticible as a YO, but do leave a small 'bar' on the front of the work.. (and the lift bar or the cast on method are both less noticible!)
You should consider getting (and reading!) a good reference book about knitting to learn some of these details.
in many cases, you can interchange one increase for an other.. BUT it does change how the finished project looks..
and as a good rule, pick a style of increase, and stick to it.. consistantsy looks better (even if not the suggested increase) than inconsistancy!