I'm a new player and as said on the page is better use only gold cards lvl4 for powered up servants but as a new player this is also applicable what about lvl 1 and 2.
Or maybe I should use all my cards to powered up my actual servants to use them in the next event?
use the level 1& 2 for servant exp. They don't give anything other than minimal QP unlike the silver which give mana prisms
Golden Level 4 EXP Cards yields the biggest experience point and gets extra points when used on the corresponding Servant. Level 1 and 2 Cards obviously have lesser points, but they still get boosted a bit when used on the corresponding card.
As Servants level up, the amount of experience required grows a lot bigger. Therefore, Level 4 cards becomes the best way to reach the next level when on higher level. Level 1 and 2 cards help in raising the lower-level Servants, but as they level up, it becomes even harder for you to raise the Servants' levels with Level 1 and 2, so you're better off using higher level experience cards.
Your idea of using all your cards to power up your actual Servants is a good idea since as explained above, the only use of EXP Cards is just to raise the level of your Servants. No matter the level and the amount of the card, experience points are still experience points. You just need to decide which Servant you want to power up, and spend your EXP cards on that Servant.