Spells and ability that target are very different from those that do not. Targeting is a restriction, in that you must be able to choose legal targets of a spell or ability in order to play it. For example, you cannot play Slice in Twain just to draw a card, there must be an artifact or enchantment in play. Additionally spells that target can become countered on resolution if all of their targets are not legal when they attempt to resolve.

Spells and abilities that target will specifically say so. If the word target does not appear on the card itself or in the rules that govern the keyword, then the ability does not target. For example, Goblin Guide‘s triggered ability does not target. It instructs and potentially affects the defending player, but that does not mean it targets this player. Goblin Guide’s ability will affect a player that cannot be targeted. Similarly, the annihilator keyword ability does not target. The reminder text on cards with annihilator does not use the word ‘target’ and more importantly the portion of the comprehensive rules that covers annihilator does not use the word target.

One keyword ability that does not use reminder text and does denote targeting is enchant. Aura enchantments indicate what they can be attached to by the keyword ‘enchant blah’ in their rules text. When auras are played, they do target and you must be able to choose a legal target. This is because the sections of the comprehensive rules that governs auras and the enchant keyword ability state that aura spells target.