In Florida, currently, most construction projects require stamped drawings to obtain the building permit. This includes residential projects. "Stamped plans" are plans bearing the seal of a Registered Engineer or Architect. If you have attempted to get a permit and been informed of this, this article explains the seal (or stamp) and what is needed.
The words Engineer and Architect are capitalized because they designate licensed professions. Many people call themselves engineers, but none may call himself or herself an "Engineer" without being duly licensed. This is also true with Architects.
Architects are more protective of the word than are Engineers. A Professional Engineer carries the designation "PE" following his or her name.
Each profession has a seal. Either of these seals will suffice in Florida in most building departments. Professionals who can seal are mostly self-regulating as to what they may or may not seal. Basically one should be skilled in an area of design before he or she affixes a seal to the project.
Engineers and Architects come in all shades of ability, as do all people. The thing to do, in hunting for a professional, is to find one competent in the field encompassing what you need.
In seeking a design, it is best to hire one who is a skilled designer AND can seal the plans so you can get the permit. If you have a set of plans that you like, or have purchased, which, itself, needs a seal, then you may look for someone to stamp them. But this is something you should be very careful doing. Professionals will not simply seal plans without putting much attention and effort into the design, plans, details, etc. (though this was a rather common practice in the past and may still have some hangers-on).
But beware. You want a professional on your team. Not just someone who has a seal. The professional, if he or she considers reviewing your plans, will have to add his or her own data to the plans, and carefully go over every elements to assure that the key structural points are met.
It is best to get a licensed professional to do the entire service for you.