It is the contractor's written proof that what they intend to buy and install matches what the contract documents required.
Product data is the manufacturer's published information, marked to show exactly what is proposed. Shop drawings are drawings prepared for this project showing how the thing will actually be made or installed. Samples are the physical article, or a piece of it, when appearance or texture is being approved.
They are reviewed differently. Product data is checked against a specification. Shop drawings are checked against the design intent and against the other trades.
The design professional reviews it for conformance with the design concept and the contract documents. That is a narrower job than it sounds, and it is why a stamped submittal does not relieve the contractor of responsibility for dimensions, quantities and coordination.
Exact wording varies by project. The project manual governs, always.
Work backwards from the fabrication lead time, then add the review period the specification allows, then add one full resubmission cycle. Teams that plan for zero resubmissions plan to be late.
Generally, no. Most general conditions state clearly that a review does not authorise a change to the contract sum or time, and that deviations must be requested separately in writing. This is why an unflagged deviation inside a submittal is a problem rather than a shortcut.
It allows you to propose a substitution, on the form the specification names, by the date it names. It is not permission to quietly send a different product inside a normal submittal. Substitution procedures usually have their own deadline, and it is often earlier than the submittal itself.
From the Submittals article of the technical section for this project, not from the last project's package. That article is usually one page and it lists exactly what has to be in the envelope. Turn it into rows, tick them off, and the most common rejections stop being possible.
Read the three parts of the section in this order: Part 1 Submittals, Part 1 Quality Assurance, Part 2 Manufacturers and performance, Part 3 field quality control. Five stops, about ten minutes, and you know what to buy, what to prove, and what will be checked.