photo
(a single keyword)

photo*
(no stemming is done for you. But you can use the asterisk as a wildcard at the end of a word. This would retrieve photo, photos, photocopy, photograph, etc... The search is not case-sensitive)

photo OR sample
(logical OR: either matches)

photo AND offer
(logical AND: must match both clauses)

photo offer
(also logical AND)

photo* AND (offer* OR vendor*)
(composite. The booleans available are AND, OR, NOT)