During the game we had an argument about the meaning of "activation". On some item cards it says "during the activatiion". Does that mean they can be used ONLY during the moment of activation (flipping the activation token) or during the whole activation phase of a charecter wehen avalible? Like Bakta injection for example. Ty kindly for your replies.

"During your activation" refers to the whole activation phase. If you could only use it at the moment you activate your unit, it would say "At the start of your activation"

The figure's activation starts when a figure's controller tells it starts and ends when they say it ends. During the activation a figure can perform upto two actions and spend movement points and use during your activation abilities (like suffering upto 2 strain for movement points).

Also, note that the activation token is flipped (and deployment card exhausted) at the end of the activation, not at the beginning. (Murne Rin now has an ability where that matters.)