Here's what I do with them:
Get whole ones and keep them in the freezer, then grind a week's worth at a time and refrigerate (to keep fresher). Use ground flax on/in oatmeal, in baked goods, sprinkled on salads, in smoothies.
If you combine about 1 Tbsp ground flax and 2 Tbsp water, it makes an egg substitute for baking (as a binder, not for meringue or other uses).
If you have a dehydrator, you can make flax crackers (a raw-food staple). Either soak whole seeds, grind the seeds, or do a combo of both (try all three and see what texture you prefer). Add water (or any other liquid, like tomato juice) to the seeds or ground seeds, any other seasoning you like (Italian, Mexican), any veggies you like (diced onion, red pepper, carrot), then spread the mix on a Teflex sheet (or sheet of parchment paper) in a dehydrator, dry for a few hours, then flip the crackers onto another tray and remove the sheet and finish drying.
Chia seeds have many of the benefits of flax, but are actually nutritionally superior and their gel (the seeds + water) is very neutral tasting.