Learn English – What are the differences between “manual”, “guide” and “instruction”

There is considerable overlap among the three, and to some extent they can be interchangeable. They can be coupled together or with other terms, as in instruction manual or reference guide. In addition, there are a number of similar terms like handbook, guidebook, primer, or vade mecum.

Manual refers specifically to a reference document which provides detailed information about operation and maintenance of a product. Manufacturers will often provide an official manual for a product to provide assistance to its owners or users: cars, for example, usually come with an owner's manual, machinery with an operator's manual, and official documentation for Unix programs with manual pages.

Guide is a more generic term. Whereas manual implies a written document, one that could be a booklet for a video game or a large book for a complex product such as a car, a guide can be just a card, or in another medium altogether such as a video. It may be a detailed reference, but it can also indicate a very simple overview or instructions for a small subset of features.

Because "manual" has connotations of dense, boring text, some manufacturers or technical writers prefer the label "guide" for what would traditionally be called a "manual."

Instructions is the most generic term, and may be synonymous with directions— step-by-step guidance on how to perform a specific task or function. A manual or guide will include many sets of instructions. Used alone, however, "instructions" can refer to the simplest explanatory text— push cap and twist to open, or use other door.

The presence of user in the phrases you cited suggests an electronic or software product , in which case I would say all three phrases you cited are synonymous. For example, Apple labels the documentation section of its website as "Manuals," yet the documents themeselves are the iPhone User Guide, iPad User Guide, and so on.

I think it would be very rare to be supplied with three different references labeled user manual, user guide, and user instructions. In such a case, I would expect the manual to be the main, canonical reference; the guide to be a short overview of features; and the instructions to be the most rudimentary introduction to the use of the product in question.