Becca is a simple point and click game with a few puzzles that are all trivial to figure out. It should take you around one hour to complete it.
In case you miss one achievement, the chapter selection menu unlocked after the main story will allow you to go back and replay that specific chapter.

To obtain all the achievements, you will need to find 7 keys (one in each chapter, each of them unlocking a subsequent chapter) and 2 special items (both found in chapter 5), as well as completing all 6 chapters of the main story (the bonus chapter is not required).
The guide shows the locations for each of these items.