Pour the flaxseeds into the top of a coffee grinder until full. Many models contain a top that detaches, which you can fill, and then pour into the grinder.
Secure the lid to the grinder by twisting it clockwise on top.
Select from among the texture choices, usually fine, medium, or coarse. Select "fine" for a consistency similar to most flours.
Press the "On" button to start grinding the flaxseeds. Most models automatically grind the seeds after you select "On," and will stop when finished. Other models may require that you hold down the lid or the button to keep it grinding until it reaches the preferred consistency.
Turn the lid counterclockwise to access the ground flaxseed. Pour it into a storage container, and place in the refrigerator for up to 90 days, or use it immediately.