Decrease

Find the next two stiches (orange and yellow in the picture).

Insert your hook into the next stich (orange), yarn over and pull it under the stich.  

 You have 2 loops on your hook.

While keeping the 2 loops on your hook, insert your hook into the next stitch (yellow) yarn over and pull it under the stitch. 

You have 3 loops on your hook. 

Yarn over and pull it under the 3 loops on your hook.