Well, let's start.
PSCT (Problem-Solving Card Text) is a new sort of card texts, which was introduced in the Starter Deck: Dawn of the Xyz, where for the first time, alongside Xyz monsters, PSCT was included.
Let's look a simple card like Dimensional Prison. You all know it.
Its PSCT is as follows:
When an opponent's monster declares an attack: Target that monster; banish that target.
Okay, let's introduce you in how to properly read this sort of texts.
Everything BEFORE the colon [:] are activation requirements. These cannot he ignored.
For example, you cannot use the effect of Card Trooper during your opponent's turn. Same goes for REDMD.
Furthermore, every part AFTER the colon [:] but BEFORE the FIRST semi-colon [;] are activation costs or things that happen at activation. You must pay these before the actual card effect happens and they do not count as part of the card effect (only if costs).
As you can already guess, everything AFTER the FIRST semi-colon [;] happens at resolution of an effect, this can't be chained to.
If we now take the card I used as an example, we can see that this card exactly shows that.
When an opponent's monster declares an attack:
This part is the activation requirement(s). As we see, an opponent's monster has to declare an attack for us to use D. Prison.
Target that monster;
This part is the cost, or, in this case, things to happen at activation. You select the attacking monster. Now is the time for you or your opponent to activate card effects or cards.
banish that target.
This is the resolution if the card effect. Here, the monster will be banished.
Also, take note that some terms from the old card texts may have changed.
Examples: Remove from play -> Banish
Thank you for reading.