"The lightning flashes."
• 치네요 or 치네(요) comes from the verb 치다 (hit, strike). 쳐(요), its present tense.
• -네 is just an expletive (a word-filler to express emotions, to self and listeners) expressing awe (surprise, amazement, fear).
• Difference between plain vs expressive statement:
번개가 쳐요 (simple/plain statement of fact) - Lightning strikes.
번개가 치네요 (exclamation where speaker's emotion is added) - “Look! There's Lightning!” (or "Gasp, the lightning flashes!")