Needs

Needs["context"]loads an appropriate file if the specified context is not already in$Packages`.

Needs["context", "file"]loads file if the specified context is not already in$Packages`.

Examples

Load a package:

Needs["Developer`"]

Load with explicit file:

Needs["MyPackage`", "path/to/MyPackage.m"]

Please visit the official Wolfram Language Reference for more details.