Challah is separated after the flour and liquid are well mixed together, while the dough is still whole, before it has been divided and shaped into loaves. If the dough has been kneaded in several batches, combine it all in a single bowl.

If the conditions for reciting the blessing are met, recite the following (if you do not understand the Hebrew, you can recite the blessing in English, or in any other language you understand):

Hebrew:

Transliteration:
BA-RUCH A-TAH A-DO-NOI ELO-HAI-NU ME-LECH HA-O-LAM A-SHER KID-SHA-NU B'MITZ-VO-TAV V'TZI-VA-NU L'HAF-RISH CHAL-LAH

Translation:
Blessed are You, L-rd our G‑d, King of the Universe, who has sanctified us with His commandments and commanded us to separate challah.

Separate a small piece of dough, approximately one ounce, and say: "This is challah."

Burn the challah by wrapping it in a piece of silver foil ands placing it in the broiler, or by any other method. (If burning it inside the oven, there should be no other food baking in the oven at the same time.)