nel modo che = in the way/manner that; often interchangeable with come.
Agisci nel modo che ritieni più opportuno. Act in the way/manner that you believe to be most appropriate.
In the sentence above, nel modo che serves as a modal conjunctive phrase and explains how the action in the main clause (to act) should be executed (i.e., in an “appropriate” manner). Here are some other conjunctions and conjunctive phrases of this type:
come = like
Ho dipinto la tavola proprio come mi hai detto. I painted the table just like you told me to.
The modal constructions come se and quasi suggest that the situation expressed in the subordinate clause is hypothetical or imagined, and therefore call for a verb in the subjunctive mood.