You are good at finding hidden and inobvious things and at following tracks.
Check: you must generally be within 10 feet of the object or surface to make a search check (as per the Search skill description in the 3.5 PHB). The GM may choose to make the Search check for the character in secret, so the player doesn't know from the result whether the character has missed a hidden thing or there is nothing there. You may also use the Search skill to follow a track, but only if the DC for the task is 10 or lower.
Action: It takes a full-round action to actively search a 5-foot-by-5-foot area. In addition, although it is more difficult than actively searching a 5-foot-by-5-foot area, characters can make a Search check to passively notice small details and irregularities in objects they are near without using an action. When moving at up to one-half normal speed (that is, walking), characters take a -5 penalty to any Search check to notice a hidden door, trap or other feature within 10 feet. When moving at a speed greater than one-half but less than full speed (that is, hustling), there is a -10 penalty. It is practically impossible (-20 penalty) to passively search while running or charging.
Synergy: 5 or more ranks in Knowledge (Architecture & Engineering) gives you a +2 bonus to Search checks involving secret doors and built environments, while 5 or more ranks in Knowledge (Nature) gives you a +2 bonus to Search checks involving tracks and natural environments. These bonuses increase by +1 for every additional 10 ranks (that is, +3 at 15 ranks, +4 at 25 ranks, and so on).
Feat: the Track feat allows you to use this skill to follow tracks with a DC of greater than 10 (as per the Track feat description in the PHB).