mspirit wrote: Hi Everybody! I've recently started this game with my team the FC Gronk.

WElcome

After the acquisition of some new players I've realized that they weren't used in the previous game I had when both are clearly better than the ones that came when creating the team.

you would have to add them to the formations in the match orders and save the match orders for the game engine to use them. No automatic substitutions. In fact if one player in the match order gets injured you will end up with a randomized lineup for the game. To prevent that you need to check and save Match Orders after the weekly training and one hour before the match.

I've then noticed that there is a section for customizing the strategies of the game which makes me wonder. How does the game handles my strategies when I don't insert them?

I think it plays 80%,60%, 40% run on first 3 downs and never attempts a
Field Goal.
It defends the pass on first 2 downs and the rush on the next 2.
Of course I maynot be accurate on this one

Isn't the coach supposed to do it himself? Does not inserting your own tactics a big prejudice do your results? Do I have to create an entire playbook or is it just the starting position? Do you know any website or source of information that recommends what should be inserted?

You cannot customize your playbook.(there is not "playbook" per se). In a convoluted sense the game engine picks random plays out of a hidden playbook. The offensive and defensive customization controls are in orders tab in the 'match orders' page
Offensive customization lets you decide what % of the plays you want to run
Defensive customization helps you decide whether youd like to defend the run/pass on each down.
I hope that answers that question.

I love Football but as a foreigner only recently converted to the sport I still have difficulties facing more detailed parts of the game (that's one of the reasons I'm playing Grid Iron actually). Thank you for your help!

Welcome and read the 2 announcement threads - thats a great place to start. And if you have any questions, ask away