How can you tell the difference between a true leaf and a seed leaf?

The seed leaves are always the first set of leaves to come up out of the soil, 

for most plants they're very rounded looking 

and many plants will look almost identical at this stage.

Seed leaves nourish the new sprout until it can photosynthesize its own food. 

The first few sets of true leaves don't always look like the plant's adult foliage, but they are still considered true leaves. The first set of true leaves will be pretty obvious, you won't miss it. 

Be patient, sometimes plants will sit there with just the seed leaves for a little while.

OOOOOH, LOOK....

Beans are growing up the teepee fast now...

A baby budding string bean....the first ones.

So much is growing!!!