Although naively creatures can be thought of as the mainstay or must-have cards for every Magic deck, this is not the case. There are decks that can be built without creatures. That being said, a good grasp of what the playable creatures are is important to most Magic decks, especially those that are White, Black, and Green. There are Blue strategies of control that do not require creatures, and there are Red strategies of direct damage to the opponent using non-creature spells that also do not require creatures.
The most common creature types vary by color. The most common white creature is some type of Human, either Human, or, for example, Human Soldier.
Although naively you may want to run as many low Converted Mana Cost (CMC) creatures as possible, because after each turn you get more mana that you can use yet you are only drawing one new card per turn, it is a better strategy to run a range of creatures at different CMCs, and these creatures then fit into what is referred to as a mana curve. Here is a good range of Blue creatures. With 4 of the lower CMC cards and 3 of the higher CMC cards you would be building a mana curve that helps you from having insufficient mana to play the higher CMC cards.
These days I am weary of using too many X/1 creatures (where X can be any number) because of how many times I have been cursed by this card:
My favorite creatures are the Fatty creatures (I am a Johnny!).
