directions; instructions; usage method
Refers to the way something is used, or written instructions for use. Common in manuals, product labels, and formal contexts.
Please read the directions for this medicine carefully.
I don't understand how to use the new software.
使用法 and 用法 are both formal terms for how something is used, but 使用法 is slightly more explicit about 'method of use' and common on manuals, while 用法 is broader and also used for word usage in grammar.
Compound of 使用 (shiyō, 'use') and 法 (hō, 'method' or 'law').