Pollen will appear as yellowish dust. You will see it all over the leaves once the male flowers have begun opening up in earnest.
You can collect some by placing a small paper sack over a branch full of mature flowers, pinching the open end shut around the stem of the branch, and giving it a good shake or two... Bring the bag in and dump it out on a mirror, you should see the yellow dust.
Store pollen in an airtight container kept in a cool dry place, and it will keep for a while.