This was made by nekofjung for the nº4 lesson
I think that is a really good article
so i'll post it here for students to read it.

In yugioh, spells and traps
have 3 different speeds: 1, 2, and 3. There
are some important rules to consider about spell speeds, so let’s go over the
cards 1 at a time:





Spell Speed 1 cards include Normal, Equip, Ritual, and Field Spell cards. Ignition-type effects of monsters are also
considered to be Spell Speed 1. Spell
Speed 1 cards can only be chain link 1, so you can never chain to a card with a
Spell Speed 1 card. Unless the card
specifically mentions a timing when it can be activated, Spell Speed 1 cards
can only be activated during the Main Phases of your turn.





Spell Speed 2 cards include
Quick-Play Spells, Normal
and Continuous Traps, and Trigger-type monster effects. These cards can be chained to any Spell Speed
1 or 2 card and can be activated at any time except for a couple conditions. First, if the card specifies it may only be
activated at a specific time or when a specific condition is filled, and second
these cards cannot be activated during the Damage Step of the Battle Phase
unless the card affects a monster’s stats (i.e., Shrink, Reinforcements . . . etc). Note that Spell Speed 2 cards cannot be
chained to Spell Speed 3 cards.





The only Spell Speed 3 cards
in the game are the Counter Traps like Solemn Judgment and Forced Back. Counter Traps can be chained to any effect as
long as there is not a condition on the card for when they can be activated. Counter Traps can also be activated in the
Damage Step. The only card that can be
chained to a Counter Trap is another Counter Trap.