In a Yu-Gi-Oh!
deck you should have monster cards, spell cards and trap cards. You
should pick cards you like and also cards that work well together. For
example, I have an Elemental Hero deck and its cards mainly go with
the elemental heroes in my deck. I work on it still and am always adding
new cards, which is very important. When you've got your deck made,
don't stop there. Get other cards to power up your deck.
Spell
Cards, and Their Symbols
There are
symbols that tell you about the spell card properties, for example,
here is the symbol for a quick play spell (which means you can
activate this spell card any time during your turn):
Quick
Play Spell Card

Here
is where you'll find the symbol on the card:

If there
is no quick play symbol, you can only activate it during your main phase.
Equip
Spell Cards

An equip
spell card is one that equips (attaches) to a monster. For example,
Junk Barrage. When the equip monster destroys a monster by battle and
sends it to the graveyard, this card inflicts damage to your opponent
equal to half of the destroyed monster's attack points.
Field
Spell Cards

A field
spell card is placed in your field spell zone (the top far left)
of the playing board. Here it is able to impact the entire field. For
instance, Skyscraper.
Skyscraper's ability is that when any elemental hero monster from your
or your opponent's side of the field is attacking, and its attack is
lower than the attack of the monster it's attacking, it gains 1000 attack
points during the damage step only.
Three
other symbols for spell cards are the continuous, the counter and the
ritual.
Continuous
Spell Cards

A continuous
spell card is one that does not go to the graveyard (the discard
pile) after it is activated until it is destroyed by a card effect.
Other spell and trap cards go to the graveyard after activation unless
they are continuous as well.
Counter
Spell Cards

A counter
spell card is one that counters an opponent's ability or summon of a
monster.
Ritual
Spell Cards

A ritual
spell card is a spell card that summons a ritual monster (blue in color).
For example, White Dragon Ritual is used to summon Paladin of White
Dragon. With every Ritual Spell card you have to sacrifice monsters
that are equal in level to the ritual monster. As for Paladin of White
Dragon, you have to sacrifice monsters that add up to Level 4 or more.