If i have a poke with flash fire ability and i give him a flame orb, my fire type moves will be boosted with 50% with this item, or just from opponents fire type attack?

I believe that only fire type attacks will trigger Flash fire.

If i have a poke with flash fire ability and i give him a flame orb, my fire type moves will be boosted with 50% with this item, or just from opponents fire type attack?

Hi there. As Purp said and as quoted from Bulbapedia

Flash Fire makes the Pokémon immune to Fire-type moves and will activate when hit by one. When activated, the power of the Pokémon's Fire-type moves is increased by 50%. While subsequent hits by Fire-type moves will not provide further increases in power, the Pokémon remains immune to the moves.

This means that it will only activate when hit by a fire MOVE. Flame orb isn't a move and therefore will not trigger it.

 

Let me know if you need anything else.