This set of instruments is used for navigation at sea. Proficiency with navigator’s tools lets you chart a ship’s course and follow navigation charts. In addition, these tools allow you to add your proficiency bonus to any ability check you make to avoid getting lost at sea.
RollQuest ships the D&D 2014 SRD as a content pack, on a 5e character sheet that does the maths - roll from the sheet and let the numbers work themselves out. Free to start.