m1pr (make one purl right) is an increase worked on the purl side of the fabric between 2 stitches, forming a right slant when looked at on the knit side of the fabric. This stitch increases the total number of stitches on your needle by one.
How to work a m1pr increase
So I have cast on 10 stitches and worked a few rows in stocking stitch, on the next purl row the instructions are :
P4, m1pr, purl to end. (11 sts)
I have purled the first 4 stitches of the row and am now ready to work m1pr:
Step 1 – Insert the left hand needle from back to front into the horizontal strand between the stitches on each needle.
Step 2 – Insert the tip of the right hand needle into the front loop purlwise (from right to left), wrap yarn around (as you would with a normal purl stitch).
Step 3 – Pull yarn through, dropping the stitch of the left hand needle.
One increase completed.