If 3/3 creature with d. strike hits player it deals 6 damage in total right? But what if this creature has also trample and it's blocked by normal 1/1? Would it deal 5 dmg in total?
Yes, it would (well, it could).
You choose whether it deals 1, 2, or 3 damage to the blocking creature in the first combat damage step, with any left over damage being dealt to the player or planeswalker it is attacking.
Then, in the regular combat damage step, it deals all 3 damage to the player or planeswalker it is attacking.