There are many patterns fictional works fall into but I'll talk about four of the most common ones. Knowing the pattern you've chosen for your book can help as you plan the fictional journey for your characters.
The steady progression. In this version, the story gradually unfolds. Beginning with the introduction of the characters, setting and time. At the start the real meat of the story isn't shown but is gradually introduced. Background is woven in along with hints about what the characters will face and discover.
The spiking pattern. In this version the story rises to a high pean and then descends into a deep valley. The spikes show the main characters facing some kind of conflict. This can be physical or mental or a problem the character or characters must face. The valley shows the characters coming to grips with the decisions made. Each peak is higher than the last and the valley may be deeper or shallower. until the characters reach the end. Often this means a final dramatic scene, ending with a satisfactory ending to the story.
The roller coaster pattern. Here the tension begins with the first scene and continues until the story reaches a high peak. Then the story moves rapidly down to the ending giving the reader little time to do more but keep turning the pages.
The circular pattern is one that's hard to accomplish. The final scene must echo the opening scene. Maybe not being completely the same scene but one that reflects like a mirror showing the same feelings and emotions as the opening scene. There may or may not be a happy ending but the ending must be satisfactory.