I am making a little helmet hat for a baby. At one point it says slip 2 sts as to knit the slip them back in?

It makes a twisted decrease and is possibly part of how the pattern you are knitting is supposed to look. An easier way to do this is to put your right needle through both stitches at the same time as if you were going to knit 2 together and just slip them to the right needle, which twists them. Now, slip them back to the left needle as one stitch without twisting them again in either direction by putting the left needle in and simply moving them as one stitch. Now bring your yarn forward and purl them together. Will the type of decrease you make matter as long as you decrease? Not really, but what will matter is the visual effect of this particular decrease. I'm doing a shawl with a similar, although double, decrease right now, and the resulting decrease looks like a tent and balances the lace properly. This may not matter in the hat (unless it's a lace pattern and then it DOES, trust me) but in some stitch patterns it will matter. In lace the direction and type of decreases defines the openwork of the lace and how the visual effect of the pattern works out.

So, you are supposed to slip two stitches as if to knit, THEN replace them on the left hand needle and purl the two together? Sounds like the pattern is just getting you to twist the stitches before you decrease. Can't imagine that it will make a huge difference in the appearance, so go with what ever decreasing stitch you feel more comfortable with using.

are you trying to ask how to decrease one stitch??

the easiest way to decrease would be to insert your needle through 2 stitches at the same time and knit them together to make 1 stitch. this is a right slanting decreases in every method.

another form of decrease would be a SSK (slip, slip, knit) you slip 2 stitches knitwise and then knit them togther through the back loops. this is a left slanted decrease.

if you have any other questions feel free to email me to help with patterns or anything else on your mind.

Whether or not it makes a difference depends on your personal style of knitting. It produces a decrease that slants like this \ rather than the other way.

A plain k2tog (knit 2 together) slants to the right in some knitting styles and to the left in other methods. If your style of k2tog produces \ then you don't need the extra steps, but you would need to "slip 2 sts as to purl and slip them back in" in order to get the opposite slant (which the other style gets with k2tog).